Securities (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Securities
Available-for-sale, amortized cost	$ 368,235	$ 414,457
Available-for-sale, gross unrealized gains	3,712	1,904
Available-for-sale, gross unrealized losses	(5,921)	(14,671)
Total available-for-sale securities	366,026	401,690
Total held-to-maturity securities	2,053,337	1,849,526
Held-to-maturity, gross unrealized gains	14,310	13,023
Held-to-maturity, gross unrealized losses	(32,269)	(51,427)
Held-to-maturity securities, fair value (in dollars)	2,035,378	1,811,122
GSE issuance REMICs and CMOs
Securities
Available-for-sale, amortized cost	250,318	292,131
Available-for-sale, gross unrealized gains	3,191	1,077
Available-for-sale, gross unrealized losses	(2,763)	(7,134)
Total available-for-sale securities	250,746	286,074
Total held-to-maturity securities	1,562,719	1,474,506
Held-to-maturity, gross unrealized gains	12,793	12,877
Held-to-maturity, gross unrealized losses	(23,830)	(33,925)
Held-to-maturity securities, fair value (in dollars)	1,551,682	1,453,458
Non-GSE issuance REMICs and CMOs
Securities
Available-for-sale, amortized cost	5,685	7,516
Available-for-sale, gross unrealized gains	43	57
Available-for-sale, gross unrealized losses	(1)	(1)
Total available-for-sale securities	5,727	7,572
Total held-to-maturity securities	2,669	3,833
Held-to-maturity, gross unrealized gains	37	61
Held-to-maturity, gross unrealized losses	(7)	(10)
Held-to-maturity securities, fair value (in dollars)	2,699	3,884
GSE pass-through certificates
Securities
Available-for-sale, amortized cost	13,538	16,120
Available-for-sale, gross unrealized gains	478	770
Available-for-sale, gross unrealized losses	(5)	(2)
Total available-for-sale securities	14,011	16,888
Total held-to-maturity securities	290,152	282,473
Held-to-maturity, gross unrealized gains	1,168	85
Held-to-maturity, gross unrealized losses	(5,360)	(10,089)
Held-to-maturity securities, fair value (in dollars)	285,960	272,469
Total residential mortgage-backed securities
Securities
Available-for-sale, amortized cost	269,541	315,767
Available-for-sale, gross unrealized gains	3,712	1,904
Available-for-sale, gross unrealized losses	(2,769)	(7,137)
Total available-for-sale securities	270,484	310,534
Total held-to-maturity securities	1,855,540	1,760,812
Held-to-maturity, gross unrealized gains	13,998	13,023
Held-to-maturity, gross unrealized losses	(29,197)	(44,024)
Held-to-maturity securities, fair value (in dollars)	1,840,341	1,729,811
Obligations of GSEs
Securities
Available-for-sale, amortized cost	98,679	98,675
Available-for-sale, gross unrealized losses	(3,140)	(7,522)
Total available-for-sale securities	95,539	91,153
Total held-to-maturity securities	90,934	88,128
Held-to-maturity, gross unrealized gains	52
Held-to-maturity, gross unrealized losses	(2,531)	(7,403)
Held-to-maturity securities, fair value (in dollars)	88,455	80,725
Fannie Mae stock
Securities
Available-for-sale, amortized cost	15	15
Available-for-sale, gross unrealized losses	(12)	(12)
Total available-for-sale securities	3	3
Multi-family mortgage-backed securities:
Securities
Total held-to-maturity securities	106,326
Held-to-maturity, gross unrealized gains	260
Held-to-maturity, gross unrealized losses	(541)
Held-to-maturity securities, fair value (in dollars)	106,045
Other
Securities
Total held-to-maturity securities	537	586
Held-to-maturity securities, fair value (in dollars)	$ 537	$ 586