Quarterly report pursuant to Section 13 or 15(d)

FAIR VALUES OF ASSETS AND LIABILITIES - Recurring Basis (Details)

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FAIR VALUES OF ASSETS AND LIABILITIES - Recurring Basis (Details) - USD ($)
$ in Thousands
Jun. 30, 2016
Dec. 31, 2015
Assets measured at fair value on a recurring basis    
Loans held for investment $ 36,978 $ 32,889
Trading account securities 35,289 36,997
Available-for-sale and other securities 9,653,038 8,775,441
U.S. Treasury    
Assets measured at fair value on a recurring basis    
Available-for-sale and other securities 7,320 5,472
Federal agencies: Mortgage-backed securities    
Assets measured at fair value on a recurring basis    
Available-for-sale and other securities 5,217,792 4,521,688
Federal agencies, Other agencies    
Assets measured at fair value on a recurring basis    
Available-for-sale and other securities 85,993 115,913
Municipal securities    
Assets measured at fair value on a recurring basis    
Available-for-sale and other securities 2,581,627 2,456,396
Corporate debt    
Assets measured at fair value on a recurring basis    
Available-for-sale and other securities 520,004 466,477
Recurring Basis    
Assets measured at fair value on a recurring basis    
Loans held for sale 614,626 337,577
Trading account securities 35,289 36,997
Available-for-sale and other securities 9,319,288 8,442,655
Automobile loans 925 1,748
MSRs 13,105 17,585
Derivative assets netting (222,765) (161,297)
Derivatives assets 366,007 274,872
Liabilities measured at fair value on a recurring basis    
Gross amounts offset in the condensed consolidated balance sheets (239,910) (144,309)
Derivative liabilities 85,949 144,350
Short-term borrowings 907 1,770
Recurring Basis | U.S. Treasury    
Assets measured at fair value on a recurring basis    
Available-for-sale and other securities 7,320 5,472
Recurring Basis | Federal agencies: Mortgage-backed securities    
Assets measured at fair value on a recurring basis    
Available-for-sale and other securities 5,217,792 4,521,688
Recurring Basis | Federal agencies, Other agencies    
Assets measured at fair value on a recurring basis    
Available-for-sale and other securities 85,993 115,913
Recurring Basis | Municipal securities    
Assets measured at fair value on a recurring basis    
Trading account securities 2,894 4,159
Available-for-sale and other securities 2,581,627 2,456,396
Recurring Basis | Asset-backed Securities    
Assets measured at fair value on a recurring basis    
Available-for-sale and other securities 890,573 861,413
Recurring Basis | Corporate debt    
Assets measured at fair value on a recurring basis    
Available-for-sale and other securities 520,004 466,477
Recurring Basis | Other Debt Obligations [Member]    
Assets measured at fair value on a recurring basis    
Trading account securities 32,395 32,838
Available-for-sale and other securities 15,979 15,296
Recurring Basis | Level 1    
Assets measured at fair value on a recurring basis    
Loans held for sale 0 0
Loans held for investment 0 0
Trading account securities 32,395 32,475
Available-for-sale and other securities 19,352 16,869
Automobile loans 0 0
MSRs 0 0
Gross amounts of recognized assets 0 0
Liabilities measured at fair value on a recurring basis    
Gross amounts of recognized liabilities 0 0
Short-term borrowings 0 0
Recurring Basis | Level 1 | U.S. Treasury    
Assets measured at fair value on a recurring basis    
Available-for-sale and other securities 7,320 5,472
Recurring Basis | Level 1 | Federal agencies: Mortgage-backed securities    
Assets measured at fair value on a recurring basis    
Available-for-sale and other securities 0 0
Recurring Basis | Level 1 | Federal agencies, Other agencies    
Assets measured at fair value on a recurring basis    
Available-for-sale and other securities 0 0
Recurring Basis | Level 1 | Municipal securities    
Assets measured at fair value on a recurring basis    
Trading account securities 0 0
Available-for-sale and other securities 0 0
Recurring Basis | Level 1 | Asset-backed Securities    
Assets measured at fair value on a recurring basis    
Available-for-sale and other securities 0 0
Recurring Basis | Level 1 | Corporate debt    
Assets measured at fair value on a recurring basis    
Available-for-sale and other securities 0 0
Recurring Basis | Level 1 | Other Debt Obligations [Member]    
Assets measured at fair value on a recurring basis    
Trading account securities 32,395 32,475
Available-for-sale and other securities 12,032 11,397
Recurring Basis | Level 2    
Assets measured at fair value on a recurring basis    
Loans held for sale 614,626 337,577
Loans held for investment 36,978 32,889
Trading account securities 2,894 4,522
Available-for-sale and other securities 6,990,582 6,229,898
Automobile loans 0 0
MSRs 0 0
Gross amounts of recognized assets 573,837 429,448
Liabilities measured at fair value on a recurring basis    
Gross amounts of recognized liabilities 323,675 287,994
Short-term borrowings 907 1,770
Recurring Basis | Level 2 | U.S. Treasury    
Assets measured at fair value on a recurring basis    
Available-for-sale and other securities 0 0
Recurring Basis | Level 2 | Federal agencies: Mortgage-backed securities    
Assets measured at fair value on a recurring basis    
Available-for-sale and other securities 5,217,792 4,521,688
Recurring Basis | Level 2 | Federal agencies, Other agencies    
Assets measured at fair value on a recurring basis    
Available-for-sale and other securities 85,993 115,913
Recurring Basis | Level 2 | Municipal securities    
Assets measured at fair value on a recurring basis    
Trading account securities 2,894 4,159
Available-for-sale and other securities 343,652 360,845
Recurring Basis | Level 2 | Asset-backed Securities    
Assets measured at fair value on a recurring basis    
Available-for-sale and other securities 819,194 761,076
Recurring Basis | Level 2 | Corporate debt    
Assets measured at fair value on a recurring basis    
Available-for-sale and other securities 520,004 466,477
Recurring Basis | Level 2 | Other Debt Obligations [Member]    
Assets measured at fair value on a recurring basis    
Trading account securities 0 363
Available-for-sale and other securities 3,947 3,899
Recurring Basis | Level 3    
Assets measured at fair value on a recurring basis    
Loans held for sale 0 0
Loans held for investment 0 0
Trading account securities 0 0
Available-for-sale and other securities 2,309,354 2,195,888
Automobile loans 925 1,748
MSRs 13,105 17,585
Gross amounts of recognized assets 14,935 6,721
Liabilities measured at fair value on a recurring basis    
Gross amounts of recognized liabilities 2,184 665
Short-term borrowings 0 0
Recurring Basis | Level 3 | U.S. Treasury    
Assets measured at fair value on a recurring basis    
Available-for-sale and other securities 0 0
Recurring Basis | Level 3 | Federal agencies: Mortgage-backed securities    
Assets measured at fair value on a recurring basis    
Available-for-sale and other securities 0 0
Recurring Basis | Level 3 | Federal agencies, Other agencies    
Assets measured at fair value on a recurring basis    
Available-for-sale and other securities 0 0
Recurring Basis | Level 3 | Municipal securities    
Assets measured at fair value on a recurring basis    
Trading account securities 0 0
Available-for-sale and other securities 2,237,975 2,095,551
Recurring Basis | Level 3 | Asset-backed Securities    
Assets measured at fair value on a recurring basis    
Available-for-sale and other securities 71,379 100,337
Recurring Basis | Level 3 | Corporate debt    
Assets measured at fair value on a recurring basis    
Available-for-sale and other securities 0 0
Recurring Basis | Level 3 | Other Debt Obligations [Member]    
Assets measured at fair value on a recurring basis    
Trading account securities 0 0
Available-for-sale and other securities $ 0 $ 0