Annual report pursuant to Section 13 and 15(d)

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

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AVAILABLE-FOR-SALE AND OTHER SECURITIES - Schedule of Amortized Cost, Fair Value, and Gross Unrealized Gains/(Losses) (Details) - USD ($)
$ in Thousands
Dec. 31, 2015
Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 8,770,923 $ 9,359,886
Gross Gains 88,169 117,554
Gross Losses (83,651) (92,770)
Fair Value 8,775,441 9,384,670
U.S. Treasury securities    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 5,457 5,435
Gross Gains 15 17
Gross Losses 0 0
Fair Value 5,472 5,452
Federal agencies: Mortgage-backed    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 4,505,318 5,273,899
Gross Gains 30,078 63,906
Gross Losses (13,708) (15,104)
Fair Value 4,521,688 5,322,701
Federal agencies: Other agencies    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 115,076 349,715
Gross Gains 888 2,871
Gross Losses (51) (1,043)
Fair Value 115,913 351,543
Total U.S. Government backed agencies    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 4,625,851 5,629,049
Gross Gains 30,981 66,794
Gross Losses (13,759) (16,147)
Fair Value 4,643,073 5,679,696
Municipal securities    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 2,431,943 1,841,311
Gross Gains 51,558 37,398
Gross Losses (27,105) (10,140)
Fair Value 2,456,396 1,868,569
Private-label CMO    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost   43,730
Gross Gains   1,116
Gross Losses   (2,920)
Fair Value   41,926
Asset-backed securities    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 901,059 1,014,999
Gross Gains 535 2,061
Gross Losses (40,181) (61,062)
Fair Value 861,413 955,998
Corporate debt    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 464,207 479,151
Gross Gains 4,824 9,442
Gross Losses (2,554) (2,417)
Fair Value 466,477 486,176
Other securities    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 347,863 351,646
Gross Gains 271 743
Gross Losses (52) (84)
Fair Value $ 348,082 $ 352,305