Quarterly report pursuant to Section 13 or 15(d)

AVAILABLE-FOR-SALE AND OTHER SECURITIES - Schedule of Amortized Cost, Fair Value, and Gross Unrealized Gains and Losses (Details)

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AVAILABLE-FOR-SALE AND OTHER SECURITIES - Schedule of Amortized Cost, Fair Value, and Gross Unrealized Gains and Losses (Details) - USD ($)
$ in Thousands
Mar. 31, 2016
Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 9,238,387 $ 8,770,923
Unrealized Gross Gains 160,823 88,169
Unrealized Gross Losses (79,829) (83,651)
Fair Value 9,319,381 8,775,441
U.S. Treasury    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 6,261 5,457
Unrealized Gross Gains 46 15
Unrealized Gross Losses 0 0
Fair Value 6,307 5,472
Federal agencies: Mortgage-backed securities    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 4,768,869 4,505,318
Unrealized Gross Gains 74,186 30,078
Unrealized Gross Losses (1,063) (13,708)
Fair Value 4,841,992 4,521,688
Federal agencies, Other agencies    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 111,455 115,076
Unrealized Gross Gains 3,041 888
Unrealized Gross Losses 0 (51)
Fair Value 114,496 115,913
Total U.S. Treasury, Federal agency securities    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 4,886,585 4,625,851
Unrealized Gross Gains 77,273 30,981
Unrealized Gross Losses (1,063) (13,759)
Fair Value 4,962,795 4,643,073
Municipal securities    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 2,595,466 2,431,943
Unrealized Gross Gains 72,956 51,558
Unrealized Gross Losses (34,666) (27,105)
Fair Value 2,633,756 2,456,396
Asset-backed securities    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 879,616 901,059
Unrealized Gross Gains 1,724 535
Unrealized Gross Losses (43,966) (40,181)
Fair Value 837,374 861,413
Corporate debt    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 528,280 464,207
Unrealized Gross Gains 8,495 4,824
Unrealized Gross Losses (114) (2,554)
Fair Value 536,661 466,477
Other securities    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 348,440 347,863
Unrealized Gross Gains 375 271
Unrealized Gross Losses (20) (52)
Fair Value $ 348,795 $ 348,082