Securities (Details 2) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Securities
Available-for-sale, less than twelve months, estimated fair value	$ 100,104	$ 45,226
Available-for-sale, less than twelve months, gross unrealized losses	(955)	(555)
Available-for-sale, twelve months or longer, estimated fair value	72,886	147,718
Available-for-sale, twelve months or longer, gross unrealized losses	(982)	(2,999)
Available-for-sale, total, estimated fair value	172,990	192,944
Available-for-sale, total, gross unrealized losses	(1,937)	(3,554)
Held-to-maturity, less than twelve months, estimated fair value	107,317	222,216
Held-to-maturity securities, continuous unrealized loss position, less than 12 months, accumulated loss	(396)	(892)
Held-to-maturity, twelve months or longer, estimated fair value	484,923	744,508
Held-to-maturity securities, continuous unrealized loss position, 12 months or longer, accumulated loss	(8,963)	(19,146)
Held-to-maturity, total, estimated fair value	592,240	966,724
Held-to-maturity, total, gross unrealized losses	(9,359)	(20,038)
GSE issuance REMICs and CMOs
Securities
Available-for-sale, less than twelve months, estimated fair value	75,161	20,587
Available-for-sale, less than twelve months, gross unrealized losses	(829)	(159)
Available-for-sale, twelve months or longer, estimated fair value	0	75,444
Available-for-sale, twelve months or longer, gross unrealized losses	0	(1,397)
Available-for-sale, total, estimated fair value	75,161	96,031
Available-for-sale, total, gross unrealized losses	(829)	(1,556)
Held-to-maturity, less than twelve months, estimated fair value	52,357	121,861
Held-to-maturity securities, continuous unrealized loss position, less than 12 months, accumulated loss	(294)	(302)
Held-to-maturity, twelve months or longer, estimated fair value	339,709	500,348
Held-to-maturity securities, continuous unrealized loss position, 12 months or longer, accumulated loss	(6,844)	(13,739)
Held-to-maturity, total, estimated fair value	392,066	622,209
Held-to-maturity, total, gross unrealized losses	(7,138)	(14,041)
Non-GSE issuance REMICs and CMOs
Securities
Available-for-sale, twelve months or longer, estimated fair value	89	96
Available-for-sale, twelve months or longer, gross unrealized losses	(1)	(1)
Available-for-sale, total, estimated fair value	89	96
Available-for-sale, total, gross unrealized losses	(1)	(1)
Held-to-maturity, less than twelve months, estimated fair value		0
Held-to-maturity securities, continuous unrealized loss position, less than 12 months, accumulated loss		0
Held-to-maturity, twelve months or longer, estimated fair value	294	294
Held-to-maturity securities, continuous unrealized loss position, 12 months or longer, accumulated loss	(7)	(7)
Held-to-maturity, total, estimated fair value	294	294
Held-to-maturity, total, gross unrealized losses	(7)	(7)
GSE pass-through certificates
Securities
Available-for-sale, less than twelve months, estimated fair value	86	53
Available-for-sale, less than twelve months, gross unrealized losses	(1)	(1)
Available-for-sale, twelve months or longer, estimated fair value	63	64
Available-for-sale, twelve months or longer, gross unrealized losses	(1)	(1)
Available-for-sale, total, estimated fair value	149	117
Available-for-sale, total, gross unrealized losses	(2)	(2)
Held-to-maturity, less than twelve months, estimated fair value		0
Held-to-maturity securities, continuous unrealized loss position, less than 12 months, accumulated loss		0
Held-to-maturity, twelve months or longer, estimated fair value	120,367	164,453
Held-to-maturity securities, continuous unrealized loss position, 12 months or longer, accumulated loss	(1,665)	(3,877)
Held-to-maturity, total, estimated fair value	120,367	164,453
Held-to-maturity, total, gross unrealized losses	(1,665)	(3,877)
Obligations of GSEs
Securities
Available-for-sale, less than twelve months, estimated fair value	24,857	24,586
Available-for-sale, less than twelve months, gross unrealized losses	(125)	(395)
Available-for-sale, twelve months or longer, estimated fair value	72,732	72,112
Available-for-sale, twelve months or longer, gross unrealized losses	(967)	(1,587)
Available-for-sale, total, estimated fair value	97,589	96,698
Available-for-sale, total, gross unrealized losses	(1,092)	(1,982)
Held-to-maturity, less than twelve months, estimated fair value	29,947	0
Held-to-maturity securities, continuous unrealized loss position, less than 12 months, accumulated loss	(29)	0
Held-to-maturity, twelve months or longer, estimated fair value	24,553	79,413
Held-to-maturity securities, continuous unrealized loss position, 12 months or longer, accumulated loss	(447)	(1,523)
Held-to-maturity, total, estimated fair value	54,500	79,413
Held-to-maturity, total, gross unrealized losses	(476)	(1,523)
Fannie Mae stock
Securities
Available-for-sale, twelve months or longer, estimated fair value	2	2
Available-for-sale, twelve months or longer, gross unrealized losses	(13)	(13)
Available-for-sale, total, estimated fair value	2	2
Available-for-sale, total, gross unrealized losses	(13)	(13)
Multi-family mortgage-backed securities:
Securities
Held-to-maturity, less than twelve months, estimated fair value	25,013	100,355
Held-to-maturity securities, continuous unrealized loss position, less than 12 months, accumulated loss	(73)	(590)
Held-to-maturity, total, estimated fair value	25,013	100,355
Held-to-maturity, total, gross unrealized losses	$ (73)	$ (590)