Securities (Details 2) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Securities
Available-for-sale, Less Than Twelve Months, Estimated Fair Value	$ 280,237	$ 92,893
Available-for-sale, Less Than Twelve Months, Gross Unrealized Losses	(8,790)	(589)
Available-for-sale, Twelve Months or Longer, Estimated Fair Value	8,758	10,756
Available-for-sale, Twelve Months or Longer, Gross Unrealized Losses	(51)	(102)
Available-for-sale, Total, Estimated Fair Value	288,995	103,649
Available-for-sale, Total, Gross Unrealized Losses	(8,841)	(691)
Held-to-maturity, Less Than Twelve Months, Estimated Fair Value	928,087	413,699
Held-to-maturity, Less Than Twelve Months, Gross Unrealized Losses	(27,862)	(2,760)
Held-to-maturity, Twelve Months or Longer, Estimated Fair Value	37,945	12,259
Held-to-maturity, Twelve Months or Longer, Gross Unrealized Losses	(272)	(196)
Held-to-maturity, Total, Estimated Fair Value	966,032	425,958
Held-to-maturity, Total, Gross Unrealized Losses	(28,134)	(2,956)
GSE issuance REMICs and CMOs
Securities
Available-for-sale, Less Than Twelve Months, Estimated Fair Value	186,581	67,841
Available-for-sale, Less Than Twelve Months, Gross Unrealized Losses	(3,605)	(583)
Available-for-sale, Total, Estimated Fair Value	186,581	67,841
Available-for-sale, Total, Gross Unrealized Losses	(3,605)	(583)
Held-to-maturity, Less Than Twelve Months, Estimated Fair Value	662,993	413,651
Held-to-maturity, Less Than Twelve Months, Gross Unrealized Losses	(16,638)	(2,759)
Held-to-maturity, Twelve Months or Longer, Estimated Fair Value	37,945	12,259
Held-to-maturity, Twelve Months or Longer, Gross Unrealized Losses	(272)	(196)
Held-to-maturity, Total, Estimated Fair Value	700,938	425,910
Held-to-maturity, Total, Gross Unrealized Losses	(16,910)	(2,955)
Non-GSE issuance REMICs and CMOs
Securities
Available-for-sale, Twelve Months or Longer, Estimated Fair Value	8,712	10,709
Available-for-sale, Twelve Months or Longer, Gross Unrealized Losses	(36)	(86)
Available-for-sale, Total, Estimated Fair Value	8,712	10,709
Available-for-sale, Total, Gross Unrealized Losses	(36)	(86)
GSE pass-through certificates
Securities
Available-for-sale, Less Than Twelve Months, Estimated Fair Value	167	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	212	104
Available-for-sale, Total, Gross Unrealized Losses	(2)	(2)
Held-to-maturity, Less Than Twelve Months, Estimated Fair Value	188,174	48
Held-to-maturity, Less Than Twelve Months, Gross Unrealized Losses	(7,220)	(1)
Held-to-maturity, Total, Estimated Fair Value	188,174	48
Held-to-maturity, Total, Gross Unrealized Losses	(7,220)	(1)
Obligations of GSEs
Securities
Available-for-sale, Less Than Twelve Months, Estimated Fair Value	93,489	24,995
Available-for-sale, Less Than Twelve Months, Gross Unrealized Losses	(5,184)	(5)
Available-for-sale, Total, Estimated Fair Value	93,489	24,995
Available-for-sale, Total, Gross Unrealized Losses	(5,184)	(5)
Held-to-maturity, Less Than Twelve Months, Estimated Fair Value	76,920
Held-to-maturity, Less Than Twelve Months, Gross Unrealized Losses	(4,004)
Held-to-maturity, Total, Estimated Fair Value	76,920
Held-to-maturity, Total, Gross Unrealized Losses	(4,004)
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)