Securities - Schedule of Amortized Cost and Estimated Fair Value of Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Available-for-sale:
Amortized Cost	$ 282,200	$ 418,644
Gross Unrealized Gains	1,690	2,872
Gross Unrealized Losses	(3,845)	(4,718)
Estimated Fair Value	280,045	416,798
Held-to-maturity:
Total held-to-maturity securities	2,740,132	2,296,799
Gross Unrealized Gains	5,978	11,146
Gross Unrealized Losses	(55,564)	(21,853)
Estimated Fair Value	2,690,546	2,286,092
GSE issuance REMICs and CMOs
Available-for-sale:
Amortized Cost	242,172	331,099
Gross Unrealized Gains	1,327	2,374
Gross Unrealized Losses	(2,706)	(2,934)
Estimated Fair Value	240,793	330,539
Held-to-maturity:
Total held-to-maturity securities	1,119,175	1,361,907
Gross Unrealized Gains	4,896	8,135
Gross Unrealized Losses	(11,957)	(14,128)
Estimated Fair Value	1,112,114	1,355,914
Non-GSE issuance REMICs and CMOs
Available-for-sale:
Amortized Cost	1,442	3,048
Gross Unrealized Gains	2	13
Gross Unrealized Losses	(1)	(7)
Estimated Fair Value	1,443	3,054
Held-to-maturity:
Total held-to-maturity securities	193	198
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(7)	(5)
Estimated Fair Value	186	193
GSE pass-through certificates
Available-for-sale:
Amortized Cost	8,571	10,781
Gross Unrealized Gains	361	485
Gross Unrealized Losses	(2)	(2)
Estimated Fair Value	8,930	11,264
Held-to-maturity:
Total held-to-maturity securities	228,976	260,707
Gross Unrealized Gains	665	1,535
Gross Unrealized Losses	(3,282)	(3,413)
Estimated Fair Value	226,359	258,829
Total residential mortgage-backed securities
Available-for-sale:
Amortized Cost	252,185	344,928
Gross Unrealized Gains	1,690	2,872
Gross Unrealized Losses	(2,709)	(2,943)
Estimated Fair Value	251,166	344,857
Held-to-maturity:
Total held-to-maturity securities	1,348,344	1,622,812
Gross Unrealized Gains	5,561	9,670
Gross Unrealized Losses	(15,246)	(17,546)
Estimated Fair Value	1,338,659	1,614,936
Obligations of GSEs
Available-for-sale:
Amortized Cost	30,000	73,701
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1,125)	(1,762)
Estimated Fair Value	28,875	71,939
Held-to-maturity:
Total held-to-maturity securities	384,325	178,967
Gross Unrealized Gains	54	220
Gross Unrealized Losses	(16,510)	(480)
Estimated Fair Value	367,869	178,707
Fannie Mae stock
Available-for-sale:
Amortized Cost	15	15
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(11)	(13)
Estimated Fair Value	4	2
GSE issuance REMICs
Held-to-maturity:
Total held-to-maturity securities	927,119	434,587
Gross Unrealized Gains	363	1,255
Gross Unrealized Losses	(19,290)	(2,334)
Estimated Fair Value	908,192	433,508
Corporate debt securities
Held-to-maturity:
Total held-to-maturity securities	80,000	60,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(4,518)	(1,493)
Estimated Fair Value	75,482	58,507
Other
Held-to-maturity:
Total held-to-maturity securities	344	433
Gross Unrealized Gains	0	1
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 344	$ 434