Securities (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Securities
Available-for-sale, amortized cost	$ 330,481,000	$ 327,137,000
Available-for-sale, Gross Unrealized Gains	6,510,000	17,365,000
Available-for-sale, Gross Unrealized Losses	(691,000)	(315,000)
Total available-for-sale securities	336,300,000	344,187,000
Held-to-maturity, amortized cost	1,700,141,000	2,130,804,000
Held-to-maturity, Gross Unrealized Gains	27,905,000	46,268,000
Held-to-maturity, Gross Unrealized Losses	(2,956,000)	(147,000)
Held-to-maturity, estimated fair value	1,725,090,000	2,176,925,000
Residential mortgage-backed securities
Securities
Available-for-sale, amortized cost	231,796,000	327,122,000
Available-for-sale, Gross Unrealized Gains	6,296,000	12,785,000
Available-for-sale, Gross Unrealized Losses	(671,000)	(300,000)
Total available-for-sale securities	237,421,000	339,607,000
Held-to-maturity, amortized cost	1,699,485,000	2,069,960,000
Held-to-maturity, Gross Unrealized Gains	27,905,000	46,045,000
Held-to-maturity, Gross Unrealized Losses	(2,956,000)	(147,000)
Held-to-maturity, estimated fair value	1,724,434,000	2,115,858,000
GSE issuance REMICs and CMOs
Securities
Available-for-sale, amortized cost	200,152,000	286,862,000
Available-for-sale, Gross Unrealized Gains	5,258,000	11,759,000
Available-for-sale, Gross Unrealized Losses	(583,000)	(1,000)
Total available-for-sale securities	204,827,000	298,620,000
Held-to-maturity, amortized cost	1,693,437,000	2,054,380,000
Held-to-maturity, Gross Unrealized Gains	27,787,000	45,929,000
Held-to-maturity, Gross Unrealized Losses	(2,955,000)	(146,000)
Held-to-maturity, estimated fair value	1,718,269,000	2,100,163,000
Non-GSE issuance REMICs and CMOs
Securities
Available-for-sale, amortized cost	11,296,000	16,092,000
Available-for-sale, Gross Unrealized Gains	9,000
Available-for-sale, Gross Unrealized Losses	(86,000)	(297,000)
Total available-for-sale securities	11,219,000	15,795,000
Held-to-maturity, amortized cost	5,791,000	15,105,000
Held-to-maturity, Gross Unrealized Gains	112,000	92,000
Held-to-maturity, Gross Unrealized Losses		(1,000)
Held-to-maturity, estimated fair value	5,903,000	15,196,000
GSE pass-through certificates
Securities
Available-for-sale, amortized cost	20,348,000	24,168,000
Available-for-sale, Gross Unrealized Gains	1,029,000	1,026,000
Available-for-sale, Gross Unrealized Losses	(2,000)	(2,000)
Total available-for-sale securities	21,375,000	25,192,000
Held-to-maturity, amortized cost	257,000	475,000
Held-to-maturity, Gross Unrealized Gains	6,000	24,000
Held-to-maturity, Gross Unrealized Losses	(1,000)
Held-to-maturity, estimated fair value	262,000	499,000
Obligations of GSEs
Securities
Available-for-sale, amortized cost	98,670,000
Available-for-sale, Gross Unrealized Gains	214,000
Available-for-sale, Gross Unrealized Losses	(5,000)
Total available-for-sale securities	98,879,000
Held-to-maturity, amortized cost		57,868,000
Held-to-maturity, Gross Unrealized Gains		140,000
Held-to-maturity, estimated fair value		58,008,000
Freddie Mac and Fannie Mae stock
Securities
Available-for-sale, amortized cost	15,000	15,000
Available-for-sale, Gross Unrealized Gains		4,580,000
Available-for-sale, Gross Unrealized Losses	(15,000)	(15,000)
Total available-for-sale securities		4,580,000
Obligations of states and political subdivisions
Securities
Held-to-maturity, amortized cost		2,976,000
Held-to-maturity, Gross Unrealized Gains		83,000
Held-to-maturity, estimated fair value		3,059,000
Other
Securities
Held-to-maturity, amortized cost	656,000
Held-to-maturity, estimated fair value	$ 656,000