Securities - Schedule of Amortized Cost and Estimated Fair Value of Available-for-Sale and Held-to-Maturity Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Available-for-sale:
Amortized Cost	$ 268,762	$ 282,200
Gross Unrealized Gains	1,650	1,690
Gross Unrealized Losses	(4,513)	(3,845)
Estimated Fair Value	265,899	280,045
Held-to-maturity:
Total held-to-maturity securities	2,769,376	2,740,132
Gross Unrealized Gains	6,042	5,978
Gross Unrealized Losses	(53,695)	(55,564)
Estimated Fair Value	2,721,723	2,690,546
GSE issuance REMICs and CMOs
Available-for-sale:
Amortized Cost	229,367	242,172
Gross Unrealized Gains	1,311	1,327
Gross Unrealized Losses	(3,386)	(2,706)
Estimated Fair Value	227,292	240,793
Held-to-maturity:
Total held-to-maturity securities	1,182,307	1,119,175
Gross Unrealized Gains	4,893	4,896
Gross Unrealized Losses	(11,311)	(11,957)
Estimated Fair Value	1,175,889	1,112,114
Non-GSE issuance REMICs and CMOs
Available-for-sale:
Amortized Cost	1,141	1,442
Gross Unrealized Gains	0	2
Gross Unrealized Losses	(5)	(1)
Estimated Fair Value	1,136	1,443
Held-to-maturity:
Total held-to-maturity securities	191	193
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(7)	(7)
Estimated Fair Value	184	186
GSE pass-through certificates
Available-for-sale:
Amortized Cost	8,239	8,571
Gross Unrealized Gains	339	361
Gross Unrealized Losses	(2)	(2)
Estimated Fair Value	8,576	8,930
Held-to-maturity:
Total held-to-maturity securities	221,058	228,976
Gross Unrealized Gains	909	665
Gross Unrealized Losses	(2,384)	(3,282)
Estimated Fair Value	219,583	226,359
Total residential mortgage-backed securities
Available-for-sale:
Amortized Cost	238,747	252,185
Gross Unrealized Gains	1,650	1,690
Gross Unrealized Losses	(3,393)	(2,709)
Estimated Fair Value	237,004	251,166
Held-to-maturity:
Total held-to-maturity securities	1,403,556	1,348,344
Gross Unrealized Gains	5,802	5,561
Gross Unrealized Losses	(13,702)	(15,246)
Estimated Fair Value	1,395,656	1,338,659
Obligations of GSEs
Available-for-sale:
Amortized Cost	30,000	30,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1,107)	(1,125)
Estimated Fair Value	28,893	28,875
Held-to-maturity:
Total held-to-maturity securities	379,316	384,325
Gross Unrealized Gains	23	54
Gross Unrealized Losses	(16,249)	(16,510)
Estimated Fair Value	363,090	367,869
Fannie Mae stock
Available-for-sale:
Amortized Cost	15	15
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(13)	(11)
Estimated Fair Value	2	4
GSE issuance REMICs
Held-to-maturity:
Total held-to-maturity securities	906,183	927,119
Gross Unrealized Gains	217	363
Gross Unrealized Losses	(19,581)	(19,290)
Estimated Fair Value	886,819	908,192
Corporate Debt securities
Held-to-maturity:
Total held-to-maturity securities	80,000	80,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(4,163)	(4,518)
Estimated Fair Value	75,837	75,482
Other
Held-to-maturity:
Total held-to-maturity securities	321	344
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 321	$ 344