Securities (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Securities
Available-for-sale, amortized cost	$ 424,216	$ 330,481
Available-for-sale, Gross Unrealized Gains	3,187	6,510
Available-for-sale, Gross Unrealized Losses	(11,653)	(691)
Total available-for-sale securities	415,750	336,300
Held-to-maturity, amortized cost	1,915,461	1,700,141
Held-to-maturity, Gross Unrealized Gains	17,217	27,905
Held-to-maturity, Gross Unrealized Losses	(35,907)	(2,956)
Held-to-maturity, estimated fair value	1,896,771	1,725,090
Residential mortgage-backed securities
Securities
Available-for-sale, amortized cost	325,527	231,796
Available-for-sale, Gross Unrealized Gains	3,187	6,296
Available-for-sale, Gross Unrealized Losses	(5,395)	(671)
Total available-for-sale securities	323,319	237,421
Held-to-maturity, amortized cost	1,826,730	1,699,485
Held-to-maturity, Gross Unrealized Gains	17,217	27,905
Held-to-maturity, Gross Unrealized Losses	(29,581)	(2,956)
Held-to-maturity, estimated fair value	1,814,366	1,724,434
GSE issuance REMICs and CMOs
Securities
Available-for-sale, amortized cost	300,047	200,152
Available-for-sale, Gross Unrealized Gains	2,310	5,258
Available-for-sale, Gross Unrealized Losses	(5,391)	(583)
Total available-for-sale securities	296,966	204,827
Held-to-maturity, amortized cost	1,534,021	1,693,437
Held-to-maturity, Gross Unrealized Gains	16,264	27,787
Held-to-maturity, Gross Unrealized Losses	(21,336)	(2,955)
Held-to-maturity, estimated fair value	1,528,949	1,718,269
Non-GSE issuance REMICs and CMOs
Securities
Available-for-sale, amortized cost	8,330	11,296
Available-for-sale, Gross Unrealized Gains	67	9
Available-for-sale, Gross Unrealized Losses	(1)	(86)
Total available-for-sale securities	8,396	11,219
Held-to-maturity, amortized cost	4,054	5,791
Held-to-maturity, Gross Unrealized Gains	69	112
Held-to-maturity, Gross Unrealized Losses	(10)
Held-to-maturity, estimated fair value	4,113	5,903
GSE pass-through certificates
Securities
Available-for-sale, amortized cost	17,150	20,348
Available-for-sale, Gross Unrealized Gains	810	1,029
Available-for-sale, Gross Unrealized Losses	(3)	(2)
Total available-for-sale securities	17,957	21,375
Held-to-maturity, amortized cost	288,655	257
Held-to-maturity, Gross Unrealized Gains	884	6
Held-to-maturity, Gross Unrealized Losses	(8,235)	(1)
Held-to-maturity, estimated fair value	281,304	262
Obligations of GSEs
Securities
Available-for-sale, amortized cost	98,674	98,670
Available-for-sale, Gross Unrealized Gains		214
Available-for-sale, Gross Unrealized Losses	(6,244)	(5)
Total available-for-sale securities	92,430	98,879
Held-to-maturity, amortized cost	88,127
Held-to-maturity, Gross Unrealized Losses	(6,326)
Held-to-maturity, estimated fair value	81,801
Fannie Mae stock
Securities
Available-for-sale, amortized cost	15	15
Available-for-sale, Gross Unrealized Losses	(14)	(15)
Total available-for-sale securities	1
Other
Securities
Held-to-maturity, amortized cost	604	656
Held-to-maturity, estimated fair value	$ 604	$ 656