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, 2016
Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 15,776,855 $ 8,770,923
Gross Gains 47,626 88,169
Gross Losses (261,644) (83,651)
Fair Value 15,562,837 8,775,441
U.S. Treasury securities    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 5,480 5,457
Gross Gains 17 15
Gross Losses 0 0
Fair Value 5,497 5,472
Federal agencies: Mortgage-backed    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 10,851,461 4,505,318
Gross Gains 12,548 30,078
Gross Losses (190,667) (13,708)
Fair Value 10,673,342 4,521,688
Federal agencies: Other agencies    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 73,012 115,076
Gross Gains 536 888
Gross Losses (6) (51)
Fair Value 73,542 115,913
Total U.S. Government backed agencies    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 10,929,953 4,625,851
Gross Gains 13,101 30,981
Gross Losses (190,673) (13,759)
Fair Value 10,752,381 4,643,073
Municipal securities    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 3,260,428 2,431,943
Gross Gains 28,431 51,558
Gross Losses (38,802) (27,105)
Fair Value 3,250,057 2,456,396
Asset-backed securities    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 824,124 901,059
Gross Gains 1,492 535
Gross Losses (32,135) (40,181)
Fair Value 793,481 861,413
Corporate debt    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 194,537 464,207
Gross Gains 4,161 4,824
Gross Losses (15) (2,554)
Fair Value 198,683 466,477
Other securities    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 567,813 347,863
Gross Gains 441 271
Gross Losses (19) (52)
Fair Value $ 568,235 $ 348,082