Securities (Estimated Fair Values of Securities With Gross Unrealized Losses) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Available-for-sale:
Available-for-sale, less than twelve months, estimated fair value	$ 144,235	$ 45,226
Available-for-sale, less than twelve months, gross unrealized losses	(2,731)	(555)
Available-for-sale, twelve months or longer, estimated fair value	71,718	147,718
Available-for-sale, twelve months or longer, gross unrealized losses	(2,178)	(2,999)
Available-for-sale, total, estimated fair value	215,953	192,944
Available-for-sale, total, gross unrealized losses	(4,909)	(3,554)
Held-to-maturity:
Held-to-maturity, less than twelve months, estimated fair value	643,890	222,216
Held-to-maturity securities, continuous unrealized loss position, less than 12 months, accumulated loss	(5,639)	(892)
Held-to-maturity, twelve months or longer, estimated fair value	457,778	744,508
Held-to-maturity securities, continuous unrealized loss position, 12 months or longer, accumulated loss	(15,948)	(19,146)
Held-to-maturity, total, estimated fair value	1,101,668	966,724
Held-to-maturity, total, gross unrealized losses	(21,587)	(20,038)
GSE issuance REMICs and CMOs
Available-for-sale:
Available-for-sale, less than twelve months, estimated fair value	119,668	20,587
Available-for-sale, less than twelve months, gross unrealized losses	(2,238)	(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	119,668	96,031
Available-for-sale, total, gross unrealized losses	(2,238)	(1,556)
Held-to-maturity:
Held-to-maturity, less than twelve months, estimated fair value	378,600	121,861
Held-to-maturity securities, continuous unrealized loss position, less than 12 months, accumulated loss	(2,836)	(302)
Held-to-maturity, twelve months or longer, estimated fair value	317,649	500,348
Held-to-maturity securities, continuous unrealized loss position, 12 months or longer, accumulated loss	(12,445)	(13,739)
Held-to-maturity, total, estimated fair value	696,249	622,209
Held-to-maturity, total, gross unrealized losses	(15,281)	(14,041)
Non-GSE issuance REMICs and CMOs
Available-for-sale:
Available-for-sale, less than twelve months, estimated fair value	32
Available-for-sale, less than twelve months, gross unrealized losses	(1)
Available-for-sale, twelve months or longer, estimated fair value	83	96
Available-for-sale, twelve months or longer, gross unrealized losses	(1)	(1)
Available-for-sale, total, estimated fair value	115	96
Available-for-sale, total, gross unrealized losses	(2)	(1)
Held-to-maturity:
Held-to-maturity, twelve months or longer, estimated fair value	291	294
Held-to-maturity securities, continuous unrealized loss position, 12 months or longer, accumulated loss	(7)	(7)
Held-to-maturity, total, estimated fair value	291	294
Held-to-maturity, total, gross unrealized losses	(7)	(7)
GSE pass-through certificates
Available-for-sale:
Available-for-sale, less than twelve months, estimated fair value	43	53
Available-for-sale, less than twelve months, gross unrealized losses	(1)	(1)
Available-for-sale, twelve months or longer, estimated fair value	97	64
Available-for-sale, twelve months or longer, gross unrealized losses	(1)	(1)
Available-for-sale, total, estimated fair value	140	117
Available-for-sale, total, gross unrealized losses	(2)	(2)
Held-to-maturity:
Held-to-maturity, less than twelve months, estimated fair value	39,186
Held-to-maturity securities, continuous unrealized loss position, less than 12 months, accumulated loss	(273)
Held-to-maturity, twelve months or longer, estimated fair value	115,769	164,453
Held-to-maturity securities, continuous unrealized loss position, 12 months or longer, accumulated loss	(2,564)	(3,877)
Held-to-maturity, total, estimated fair value	154,955	164,453
Held-to-maturity, total, gross unrealized losses	(2,837)	(3,877)
Obligations of GSEs
Available-for-sale:
Available-for-sale, less than twelve months, estimated fair value	24,492	24,586
Available-for-sale, less than twelve months, gross unrealized losses	(491)	(395)
Available-for-sale, twelve months or longer, estimated fair value	71,536	72,112
Available-for-sale, twelve months or longer, gross unrealized losses	(2,163)	(1,587)
Available-for-sale, total, estimated fair value	96,028	96,698
Available-for-sale, total, gross unrealized losses	(2,654)	(1,982)
Held-to-maturity:
Held-to-maturity, less than twelve months, estimated fair value	131,976
Held-to-maturity securities, continuous unrealized loss position, less than 12 months, accumulated loss	(1,977)
Held-to-maturity, twelve months or longer, estimated fair value	24,069	79,413
Held-to-maturity securities, continuous unrealized loss position, 12 months or longer, accumulated loss	(932)	(1,523)
Held-to-maturity, total, estimated fair value	156,045	79,413
Held-to-maturity, total, gross unrealized losses	(2,909)	(1,523)
Fannie Mae stock
Available-for-sale:
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:
Held-to-maturity:
Held-to-maturity, less than twelve months, estimated fair value	94,128	100,355
Held-to-maturity securities, continuous unrealized loss position, less than 12 months, accumulated loss	(553)	(590)
Held-to-maturity, total, estimated fair value	94,128	100,355
Held-to-maturity, total, gross unrealized losses	$ (553)	$ (590)