Securities (Details 2) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Securities
Available-for-sale, less than twelve months, estimated fair value	$ 23,010	$ 334,474
Available-for-sale, less than twelve months, gross unrealized losses	(140)	(14,657)
Available-for-sale, twelve months or longer, estimated fair value	193,495	205
Available-for-sale, twelve months or longer, gross unrealized losses	(5,781)	(14)
Available-for-sale, total, estimated fair value	216,505	334,679
Available-for-sale, total, gross unrealized losses	(5,921)	(14,671)
Held-to-maturity, less than twelve months, estimated fair value	373,430	1,031,627
Held-to-maturity securities, continuous unrealized loss position, less than 12 months, accumulated loss	(3,915)	(43,112)
Held-to-maturity, twelve months or longer, estimated fair value	730,770	151,609
Held-to-maturity securities, continuous unrealized loss position, 12 months or longer, accumulated loss	(28,354)	(8,315)
Held-to-maturity, total, estimated fair value	1,104,200	1,183,236
Held-to-maturity, total, gross unrealized losses	(32,269)	(51,427)
GSE issuance REMICs and CMOs
Securities
Available-for-sale, less than twelve months, estimated fair value	22,413	243,149
Available-for-sale, less than twelve months, gross unrealized losses	(136)	(7,134)
Available-for-sale, twelve months or longer, estimated fair value	97,773
Available-for-sale, twelve months or longer, gross unrealized losses	(2,627)
Available-for-sale, total, estimated fair value	120,186	243,149
Available-for-sale, total, gross unrealized losses	(2,763)	(7,134)
Held-to-maturity, less than twelve months, estimated fair value	300,843	719,715
Held-to-maturity securities, continuous unrealized loss position, less than 12 months, accumulated loss	(3,374)	(25,611)
Held-to-maturity, twelve months or longer, estimated fair value	483,810	151,581
Held-to-maturity securities, continuous unrealized loss position, 12 months or longer, accumulated loss	(20,456)	(8,314)
Held-to-maturity, total, estimated fair value	784,653	871,296
Held-to-maturity, total, gross unrealized losses	(23,830)	(33,925)
Non-GSE issuance REMICs and CMOs
Securities
Available-for-sale, twelve months or longer, estimated fair value	102	132
Available-for-sale, twelve months or longer, gross unrealized losses	(1)	(1)
Available-for-sale, total, estimated fair value	102	132
Available-for-sale, total, gross unrealized losses	(1)	(1)
Held-to-maturity, less than twelve months, estimated fair value		392
Held-to-maturity securities, continuous unrealized loss position, less than 12 months, accumulated loss		(10)
Held-to-maturity, twelve months or longer, estimated fair value	296
Held-to-maturity securities, continuous unrealized loss position, 12 months or longer, accumulated loss	(7)
Held-to-maturity, total, estimated fair value	296	392
Held-to-maturity, total, gross unrealized losses	(7)	(10)
GSE pass-through certificates
Securities
Available-for-sale, less than twelve months, estimated fair value	597	172
Available-for-sale, less than twelve months, gross unrealized losses	(4)	(1)
Available-for-sale, twelve months or longer, estimated fair value	78	70
Available-for-sale, twelve months or longer, gross unrealized losses	(1)	(1)
Available-for-sale, total, estimated fair value	675	242
Available-for-sale, total, gross unrealized losses	(5)	(2)
Held-to-maturity, less than twelve months, estimated fair value		230,795
Held-to-maturity securities, continuous unrealized loss position, less than 12 months, accumulated loss		(10,088)
Held-to-maturity, twelve months or longer, estimated fair value	168,261	28
Held-to-maturity securities, continuous unrealized loss position, 12 months or longer, accumulated loss	(5,360)	(1)
Held-to-maturity, total, estimated fair value	168,261	230,823
Held-to-maturity, total, gross unrealized losses	(5,360)	(10,089)
Obligations of GSEs
Securities
Available-for-sale, less than twelve months, estimated fair value		91,153
Available-for-sale, less than twelve months, gross unrealized losses		(7,522)
Available-for-sale, twelve months or longer, estimated fair value	95,539
Available-for-sale, twelve months or longer, gross unrealized losses	(3,140)
Available-for-sale, total, estimated fair value	95,539	91,153
Available-for-sale, total, gross unrealized losses	(3,140)	(7,522)
Held-to-maturity, less than twelve months, estimated fair value		80,725
Held-to-maturity securities, continuous unrealized loss position, less than 12 months, accumulated loss		(7,403)
Held-to-maturity, twelve months or longer, estimated fair value	78,403
Held-to-maturity securities, continuous unrealized loss position, 12 months or longer, accumulated loss	(2,531)
Held-to-maturity, total, estimated fair value	78,403	80,725
Held-to-maturity, total, gross unrealized losses	(2,531)	(7,403)
Fannie Mae stock
Securities
Available-for-sale, twelve months or longer, estimated fair value	3	3
Available-for-sale, twelve months or longer, gross unrealized losses	(12)	(12)
Available-for-sale, total, estimated fair value	3	3
Available-for-sale, total, gross unrealized losses	(12)	(12)
Multi-family mortgage-backed securities:
Securities
Held-to-maturity, less than twelve months, estimated fair value	72,587
Held-to-maturity securities, continuous unrealized loss position, less than 12 months, accumulated loss	(541)
Held-to-maturity, total, estimated fair value	72,587
Held-to-maturity, total, gross unrealized losses	$ (541)