Securities (Estimated Fair Values of Securities With Gross Unrealized Losses) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Available-for-sale:
Available-for-sale, less than twelve months, estimated fair value	$ 95,835	$ 45,226
Available-for-sale, less than twelve months, gross unrealized losses	(507)	(555)
Available-for-sale, twelve months or longer, estimated fair value	48,404	147,718
Available-for-sale, twelve months or longer, gross unrealized losses	(503)	(2,999)
Available-for-sale, total, estimated fair value	144,239	192,944
Available-for-sale, total, gross unrealized losses	(1,010)	(3,554)
Held-to-maturity:
Held-to-maturity, less than twelve months, estimated fair value	147,773	222,216
Held-to-maturity securities, continuous unrealized loss position, less than 12 months, accumulated loss	(868)	(892)
Held-to-maturity, twelve months or longer, estimated fair value	415,702	744,508
Held-to-maturity securities, continuous unrealized loss position, 12 months or longer, accumulated loss	(7,972)	(19,146)
Held-to-maturity, total, estimated fair value	563,475	966,724
Held-to-maturity, total, gross unrealized losses	(8,840)	(20,038)
GSE issuance REMICs and CMOs
Available-for-sale:
Available-for-sale, less than twelve months, estimated fair value	70,706	20,587
Available-for-sale, less than twelve months, gross unrealized losses	(472)	(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	70,706	96,031
Available-for-sale, total, gross unrealized losses	(472)	(1,556)
Held-to-maturity:
Held-to-maturity, less than twelve months, estimated fair value	66,064	121,861
Held-to-maturity securities, continuous unrealized loss position, less than 12 months, accumulated loss	(485)	(302)
Held-to-maturity, twelve months or longer, estimated fair value	305,095	500,348
Held-to-maturity securities, continuous unrealized loss position, 12 months or longer, accumulated loss	(6,319)	(13,739)
Held-to-maturity, total, estimated fair value	371,159	622,209
Held-to-maturity, total, gross unrealized losses	(6,804)	(14,041)
Non-GSE issuance REMICs and CMOs
Available-for-sale:
Available-for-sale, less than twelve months, estimated fair value	80
Available-for-sale, less than twelve months, gross unrealized losses	(2)
Available-for-sale, twelve months or longer, estimated fair value	70	96
Available-for-sale, twelve months or longer, gross unrealized losses	(6)	(1)
Available-for-sale, total, estimated fair value	150	96
Available-for-sale, total, gross unrealized losses	(8)	(1)
Held-to-maturity:
Held-to-maturity, twelve months or longer, estimated fair value	195	294
Held-to-maturity securities, continuous unrealized loss position, 12 months or longer, accumulated loss	(5)	(7)
Held-to-maturity, total, estimated fair value	195	294
Held-to-maturity, total, gross unrealized losses	(5)	(7)
GSE pass-through certificates
Available-for-sale:
Available-for-sale, less than twelve months, estimated fair value	97	53
Available-for-sale, less than twelve months, gross unrealized losses	(1)	(1)
Available-for-sale, twelve months or longer, estimated fair value	107	64
Available-for-sale, twelve months or longer, gross unrealized losses	(1)	(1)
Available-for-sale, total, estimated fair value	204	117
Available-for-sale, total, gross unrealized losses	(2)	(2)
Held-to-maturity:
Held-to-maturity, less than twelve months, estimated fair value	18
Held-to-maturity securities, continuous unrealized loss position, less than 12 months, accumulated loss	(1)
Held-to-maturity, twelve months or longer, estimated fair value	110,412	164,453
Held-to-maturity securities, continuous unrealized loss position, 12 months or longer, accumulated loss	(1,648)	(3,877)
Held-to-maturity, total, estimated fair value	110,430	164,453
Held-to-maturity, total, gross unrealized losses	(1,649)	(3,877)
Obligations of GSEs
Available-for-sale:
Available-for-sale, less than twelve months, estimated fair value	24,952	24,586
Available-for-sale, less than twelve months, gross unrealized losses	(32)	(395)
Available-for-sale, twelve months or longer, estimated fair value	48,225	72,112
Available-for-sale, twelve months or longer, gross unrealized losses	(483)	(1,587)
Available-for-sale, total, estimated fair value	73,177	96,698
Available-for-sale, total, gross unrealized losses	(515)	(1,982)
Held-to-maturity:
Held-to-maturity, less than twelve months, estimated fair value	51,080
Held-to-maturity securities, continuous unrealized loss position, less than 12 months, accumulated loss	(295)
Held-to-maturity, twelve months or longer, estimated fair value	0	79,413
Held-to-maturity securities, continuous unrealized loss position, 12 months or longer, accumulated loss	0	(1,523)
Held-to-maturity, total, estimated fair value	51,080	79,413
Held-to-maturity, total, gross unrealized losses	(295)	(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	10,686	100,355
Held-to-maturity securities, continuous unrealized loss position, less than 12 months, accumulated loss	(12)	(590)
Held-to-maturity, total, estimated fair value	10,686	100,355
Held-to-maturity, total, gross unrealized losses	(12)	$ (590)
Corporate debt securities
Held-to-maturity:
Held-to-maturity, less than twelve months, estimated fair value	19,925
Held-to-maturity securities, continuous unrealized loss position, less than 12 months, accumulated loss	(75)
Held-to-maturity, twelve months or longer, estimated fair value	0
Held-to-maturity securities, continuous unrealized loss position, 12 months or longer, accumulated loss	0
Held-to-maturity, total, estimated fair value	19,925
Held-to-maturity, total, gross unrealized losses	$ (75)