Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Fair Value of Financial Instruments
Total available-for-sale securities	$ 366,026	$ 401,690
Recurring basis
Fair Value of Financial Instruments
Total available-for-sale securities	366,026	401,690
Total residential mortgage-backed securities
Fair Value of Financial Instruments
Total available-for-sale securities	270,484	310,534
Total residential mortgage-backed securities | Recurring basis
Fair Value of Financial Instruments
Percentage of debt securities comprising available-for-sale portfolio	74.00%	77.00%
Available-for-sale residential mortgage-backed securities portfolio which are GSE securities (as a percent)	98.00%	98.00%
GSE issuance REMICs and CMOs
Fair Value of Financial Instruments
Total available-for-sale securities	250,746	286,074
GSE issuance REMICs and CMOs | Recurring basis
Fair Value of Financial Instruments
Total available-for-sale securities	250,746	286,074
Non-GSE issuance REMICs and CMOs
Fair Value of Financial Instruments
Total available-for-sale securities	5,727	7,572
Non-GSE issuance REMICs and CMOs | Recurring basis
Fair Value of Financial Instruments
Total available-for-sale securities	5,727	7,572
GSE pass-through certificates
Fair Value of Financial Instruments
Total available-for-sale securities	14,011	16,888
GSE pass-through certificates | Recurring basis
Fair Value of Financial Instruments
Total available-for-sale securities	14,011	16,888
Obligations of GSEs
Fair Value of Financial Instruments
Total available-for-sale securities	95,539	91,153
Obligations of GSEs | Recurring basis
Fair Value of Financial Instruments
Total available-for-sale securities	95,539	91,153
Percentage of debt securities comprising available-for-sale portfolio	26.00%	23.00%
Fannie Mae stock
Fair Value of Financial Instruments
Total available-for-sale securities	3	3
Fannie Mae stock | Recurring basis
Fair Value of Financial Instruments
Total available-for-sale securities	3	3
Level 1 | Recurring basis
Fair Value of Financial Instruments
Total available-for-sale securities	3	3
Level 1 | Fannie Mae stock | Recurring basis
Fair Value of Financial Instruments
Total available-for-sale securities	3	3
Level 2 | Recurring basis
Fair Value of Financial Instruments
Total available-for-sale securities	366,023	401,687
Level 2 | GSE issuance REMICs and CMOs | Recurring basis
Fair Value of Financial Instruments
Total available-for-sale securities	250,746	286,074
Level 2 | Non-GSE issuance REMICs and CMOs | Recurring basis
Fair Value of Financial Instruments
Total available-for-sale securities	5,727	7,572
Level 2 | GSE pass-through certificates | Recurring basis
Fair Value of Financial Instruments
Total available-for-sale securities	14,011	16,888
Level 2 | Obligations of GSEs | Recurring basis
Fair Value of Financial Instruments
Total available-for-sale securities	$ 95,539	$ 91,153