Fair Value Measurements - Carrying Value of Assets Measured at Estimated Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of available-for-sale securities	$ 416,798	$ 384,359
Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of available-for-sale securities	416,798	384,359
Total residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of available-for-sale securities	344,857	287,659
GSE issuance REMICs and CMOs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of available-for-sale securities	330,539	268,998
GSE issuance REMICs and CMOs | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of available-for-sale securities	330,539	268,998
Non-GSE issuance REMICs and CMOs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of available-for-sale securities	3,054	5,104
Non-GSE issuance REMICs and CMOs | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of available-for-sale securities	3,054	5,104
GSE pass-through certificates
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of available-for-sale securities	11,264	13,557
GSE pass-through certificates | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of available-for-sale securities	11,264	13,557
Obligations of GSEs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of available-for-sale securities	71,939	96,698
Obligations of GSEs | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of available-for-sale securities	71,939	96,698
Fannie Mae stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of available-for-sale securities	2	2
Fannie Mae stock | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of available-for-sale securities	2	2
Level 1 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of available-for-sale securities	2	2
Level 1 | GSE issuance REMICs and CMOs | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of available-for-sale securities	0	0
Level 1 | Non-GSE issuance REMICs and CMOs | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of available-for-sale securities	0	0
Level 1 | GSE pass-through certificates | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of available-for-sale securities	0	0
Level 1 | Obligations of GSEs | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of available-for-sale securities	0	0
Level 1 | Fannie Mae stock | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of available-for-sale securities	2	2
Level 2 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of available-for-sale securities	416,796	384,357
Level 2 | GSE issuance REMICs and CMOs | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of available-for-sale securities	330,539	268,998
Level 2 | Non-GSE issuance REMICs and CMOs | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of available-for-sale securities	3,054	5,104
Level 2 | GSE pass-through certificates | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of available-for-sale securities	11,264	13,557
Level 2 | Obligations of GSEs | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of available-for-sale securities	71,939	96,698
Level 2 | Fannie Mae stock | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of available-for-sale securities	$ 0	$ 0