Securities (Details 2) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Securities
Available-for-sale, Less Than Twelve Months, Estimated Fair Value	$ 88,527	$ 92,893
Available-for-sale, Less Than Twelve Months, Gross Unrealized Losses	(610)	(589)
Available-for-sale, Twelve Months or Longer, Estimated Fair Value	9,672	10,756
Available-for-sale, Twelve Months or Longer, Gross Unrealized Losses	(56)	(102)
Available-for-sale, Total, Estimated Fair Value	98,199	103,649
Available-for-sale, Total, Gross Unrealized Losses	(666)	(691)
Held-to-maturity, Less Than Twelve Months, Estimated Fair Value	460,739	413,699
Held-to-maturity, Less Than Twelve Months, Gross Unrealized Losses	(2,908)	(2,760)
Held-to-maturity, Twelve Months or Longer, Estimated Fair Value	9,212	12,259
Held-to-maturity, Twelve Months or Longer, Gross Unrealized Losses	(68)	(196)
Held-to-maturity, Total, Estimated Fair Value	469,951	425,958
Held-to-maturity, Total, Gross Unrealized Losses	(2,976)	(2,956)
GSE issuance REMICs and CMOs
Securities
Available-for-sale, Less Than Twelve Months, Estimated Fair Value	23,645	67,841
Available-for-sale, Less Than Twelve Months, Gross Unrealized Losses	(447)	(583)
Available-for-sale, Total, Estimated Fair Value	23,645	67,841
Available-for-sale, Total, Gross Unrealized Losses	(447)	(583)
Held-to-maturity, Less Than Twelve Months, Estimated Fair Value	430,788	413,651
Held-to-maturity, Less Than Twelve Months, Gross Unrealized Losses	(2,845)	(2,759)
Held-to-maturity, Twelve Months or Longer, Estimated Fair Value	9,212	12,259
Held-to-maturity, Twelve Months or Longer, Gross Unrealized Losses	(68)	(196)
Held-to-maturity, Total, Estimated Fair Value	440,000	425,910
Held-to-maturity, Total, Gross Unrealized Losses	(2,913)	(2,955)
Non-GSE issuance REMICs and CMOs
Securities
Available-for-sale, Twelve Months or Longer, Estimated Fair Value	9,626	10,709
Available-for-sale, Twelve Months or Longer, Gross Unrealized Losses	(41)	(86)
Available-for-sale, Total, Estimated Fair Value	9,626	10,709
Available-for-sale, Total, Gross Unrealized Losses	(41)	(86)
GSE pass-through certificates
Securities
Available-for-sale, Less Than Twelve Months, Estimated Fair Value	55	57
Available-for-sale, Less Than Twelve Months, Gross Unrealized Losses	(1)	(1)
Available-for-sale, Twelve Months or Longer, Estimated Fair Value	45	47
Available-for-sale, Twelve Months or Longer, Gross Unrealized Losses	(1)	(1)
Available-for-sale, Total, Estimated Fair Value	100	104
Available-for-sale, Total, Gross Unrealized Losses	(2)	(2)
Held-to-maturity, Less Than Twelve Months, Estimated Fair Value	43	48
Held-to-maturity, Less Than Twelve Months, Gross Unrealized Losses	(1)	(1)
Held-to-maturity, Total, Estimated Fair Value	43	48
Held-to-maturity, Total, Gross Unrealized Losses	(1)	(1)
Obligations of GSEs
Securities
Available-for-sale, Less Than Twelve Months, Estimated Fair Value	64,827	24,995
Available-for-sale, Less Than Twelve Months, Gross Unrealized Losses	(162)	(5)
Available-for-sale, Total, Estimated Fair Value	64,827	24,995
Available-for-sale, Total, Gross Unrealized Losses	(162)	(5)
Held-to-maturity, Less Than Twelve Months, Estimated Fair Value	29,908
Held-to-maturity, Less Than Twelve Months, Gross Unrealized Losses	(62)
Held-to-maturity, Total, Estimated Fair Value	29,908
Held-to-maturity, Total, Gross Unrealized Losses	(62)
Freddie Mac and Fannie Mae stock
Securities
Available-for-sale, Twelve Months or Longer, Estimated Fair Value	1
Available-for-sale, Twelve Months or Longer, Gross Unrealized Losses	(14)	(15)
Available-for-sale, Total, Estimated Fair Value	1
Available-for-sale, Total, Gross Unrealized Losses	$ (14)	$ (15)