Securities (Details 2) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Securities
Available-for-sale, Less Than Twelve Months, Estimated Fair Value	$ 250,219	$ 92,893
Available-for-sale, Less Than Twelve Months, Gross Unrealized Losses	(11,438)	(589)
Available-for-sale, Twelve Months or Longer, Estimated Fair Value	17,527	10,756
Available-for-sale, Twelve Months or Longer, Gross Unrealized Losses	(215)	(102)
Available-for-sale, Total, Estimated Fair Value	267,746	103,649
Available-for-sale, Total, Gross Unrealized Losses	(11,653)	(691)
Held-to-maturity, Less Than Twelve Months, Estimated Fair Value	911,991	413,699
Held-to-maturity, Less Than Twelve Months, Gross Unrealized Losses	(32,095)	(2,760)
Held-to-maturity, Twelve Months or Longer, Estimated Fair Value	78,179	12,259
Held-to-maturity, Twelve Months or Longer, Gross Unrealized Losses	(3,812)	(196)
Held-to-maturity, Total, Estimated Fair Value	990,170	425,958
Held-to-maturity, Total, Gross Unrealized Losses	(35,907)	(2,956)
Residential mortgage-backed securities
Securities
Available-for-sale, Total, Gross Unrealized Losses	(5,395)	(671)
Held-to-maturity, Total, Gross Unrealized Losses	(29,581)	(2,956)
GSE issuance REMICs and CMOs
Securities
Available-for-sale, Less Than Twelve Months, Estimated Fair Value	157,497	67,841
Available-for-sale, Less Than Twelve Months, Gross Unrealized Losses	(5,193)	(583)
Available-for-sale, Twelve Months or Longer, Estimated Fair Value	17,296
Available-for-sale, Twelve Months or Longer, Gross Unrealized Losses	(198)
Available-for-sale, Total, Estimated Fair Value	174,793	67,841
Available-for-sale, Total, Gross Unrealized Losses	(5,391)	(583)
Held-to-maturity, Less Than Twelve Months, Estimated Fair Value	647,583	413,651
Held-to-maturity, Less Than Twelve Months, Gross Unrealized Losses	(17,525)	(2,759)
Held-to-maturity, Twelve Months or Longer, Estimated Fair Value	78,148	12,259
Held-to-maturity, Twelve Months or Longer, Gross Unrealized Losses	(3,811)	(196)
Held-to-maturity, Total, Estimated Fair Value	725,731	425,910
Held-to-maturity, Total, Gross Unrealized Losses	(21,336)	(2,955)
Non-GSE issuance REMICs and CMOs
Securities
Available-for-sale, Twelve Months or Longer, Estimated Fair Value	140	10,709
Available-for-sale, Twelve Months or Longer, Gross Unrealized Losses	(1)	(86)
Available-for-sale, Total, Estimated Fair Value	140	10,709
Available-for-sale, Total, Gross Unrealized Losses	(1)	(86)
Held-to-maturity, Less Than Twelve Months, Estimated Fair Value	398
Held-to-maturity, Less Than Twelve Months, Gross Unrealized Losses	(10)
Held-to-maturity, Total, Estimated Fair Value	398
Held-to-maturity, Total, Gross Unrealized Losses	(10)
GSE pass-through certificates
Securities
Available-for-sale, Less Than Twelve Months, Estimated Fair Value	292	57
Available-for-sale, Less Than Twelve Months, Gross Unrealized Losses	(1)	(1)
Available-for-sale, Twelve Months or Longer, Estimated Fair Value	90	47
Available-for-sale, Twelve Months or Longer, Gross Unrealized Losses	(2)	(1)
Available-for-sale, Total, Estimated Fair Value	382	104
Available-for-sale, Total, Gross Unrealized Losses	(3)	(2)
Held-to-maturity, Less Than Twelve Months, Estimated Fair Value	182,209	48
Held-to-maturity, Less Than Twelve Months, Gross Unrealized Losses	(8,234)	(1)
Held-to-maturity, Twelve Months or Longer, Estimated Fair Value	31
Held-to-maturity, Twelve Months or Longer, Gross Unrealized Losses	(1)
Held-to-maturity, Total, Estimated Fair Value	182,240	48
Held-to-maturity, Total, Gross Unrealized Losses	(8,235)	(1)
Obligations of GSEs
Securities
Available-for-sale, Less Than Twelve Months, Estimated Fair Value	92,430	24,995
Available-for-sale, Less Than Twelve Months, Gross Unrealized Losses	(6,244)	(5)
Available-for-sale, Total, Estimated Fair Value	92,430	24,995
Available-for-sale, Total, Gross Unrealized Losses	(6,244)	(5)
Held-to-maturity, Less Than Twelve Months, Estimated Fair Value	81,801
Held-to-maturity, Less Than Twelve Months, Gross Unrealized Losses	(6,326)
Held-to-maturity, Total, Estimated Fair Value	81,801
Held-to-maturity, Total, Gross Unrealized Losses	(6,326)
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)