Annual report pursuant to Section 13 and 15(d)

HELD-TO-MATURITY SECURITIES - Schedule of Amortized Cost, Gross Unrealized Gains and Losses, & Fair Value (Details)

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HELD-TO-MATURITY SECURITIES - Schedule of Amortized Cost, Gross Unrealized Gains and Losses, & Fair Value (Details) - USD ($)
$ in Thousands
Dec. 31, 2015
Dec. 31, 2014
Held-to-maturity Securities [Abstract]    
Amortized Cost $ 6,159,590 $ 3,379,905
Unrealized Gross Gains 16,282 26,083
Unrealized Gross Losses (40,414) (23,273)
Fair Value 6,135,458 3,382,715
Federal agencies: Mortgage-backed    
Held-to-maturity Securities [Abstract]    
Amortized Cost 5,532,501 3,161,361
Unrealized Gross Gains 14,637 24,832
Unrealized Gross Losses (37,504) (21,736)
Fair Value 5,509,634 3,164,457
Federal agencies: Other agencies    
Held-to-maturity Securities [Abstract]    
Amortized Cost 620,052 210,563
Unrealized Gross Gains 1,645 1,251
Unrealized Gross Losses (2,786) (1,150)
Fair Value 618,911 210,664
Total U.S. Government backed agencies    
Held-to-maturity Securities [Abstract]    
Amortized Cost 6,152,553 3,371,924
Unrealized Gross Gains 16,282 26,083
Unrealized Gross Losses (40,290) (22,886)
Fair Value 6,128,545 3,375,121
Municipal securities    
Held-to-maturity Securities [Abstract]    
Amortized Cost 7,037 7,981
Unrealized Gross Gains 0 0
Unrealized Gross Losses (124) (387)
Fair Value $ 6,913 $ 7,594