Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Fair Value of Financial Instruments
Total securities available-for-sale	$ 415,750	$ 336,300
Recurring basis
Fair Value of Financial Instruments
Total securities available-for-sale	415,750	336,300
Residential mortgage-backed securities
Fair Value of Financial Instruments
Total securities available-for-sale	323,319	237,421
Residential mortgage-backed securities | Recurring basis
Fair Value of Financial Instruments
Percentage of debt securities comprising available-for-sale portfolio	78.00%	71.00%
Available-for-sale residential mortgage-backed securities portfolio which are GSE securities (as a percent)	97.00%	95.00%
GSE issuance REMICs and CMOs
Fair Value of Financial Instruments
Total securities available-for-sale	296,966	204,827
GSE issuance REMICs and CMOs | Recurring basis
Fair Value of Financial Instruments
Total securities available-for-sale	296,966	204,827
Non-GSE issuance REMICs and CMOs
Fair Value of Financial Instruments
Total securities available-for-sale	8,396	11,219
Non-GSE issuance REMICs and CMOs | Recurring basis
Fair Value of Financial Instruments
Total securities available-for-sale	8,396	11,219
GSE pass-through certificates
Fair Value of Financial Instruments
Total securities available-for-sale	17,957	21,375
GSE pass-through certificates | Recurring basis
Fair Value of Financial Instruments
Total securities available-for-sale	17,957	21,375
Obligations of GSEs
Fair Value of Financial Instruments
Total securities available-for-sale	92,430	98,879
Obligations of GSEs | Recurring basis
Fair Value of Financial Instruments
Total securities available-for-sale	92,430	98,879
Percentage of debt securities comprising available-for-sale portfolio	22.00%	29.00%
Fannie Mae stock
Fair Value of Financial Instruments
Total securities available-for-sale	1
Fannie Mae stock | Recurring basis
Fair Value of Financial Instruments
Total securities available-for-sale	1
Level 1 | Recurring basis
Fair Value of Financial Instruments
Total securities available-for-sale	1
Level 1 | Fannie Mae stock | Recurring basis
Fair Value of Financial Instruments
Total securities available-for-sale	1
Level 2 | Recurring basis
Fair Value of Financial Instruments
Total securities available-for-sale	415,749	336,300
Level 2 | GSE issuance REMICs and CMOs | Recurring basis
Fair Value of Financial Instruments
Total securities available-for-sale	296,966	204,827
Level 2 | Non-GSE issuance REMICs and CMOs | Recurring basis
Fair Value of Financial Instruments
Total securities available-for-sale	8,396	11,219
Level 2 | GSE pass-through certificates | Recurring basis
Fair Value of Financial Instruments
Total securities available-for-sale	17,957	21,375
Level 2 | Obligations of GSEs | Recurring basis
Fair Value of Financial Instruments
Total securities available-for-sale	$ 92,430	$ 98,879