Reverse Repurchase Agreements (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Long-term Debt, Fiscal Year Maturity [Abstract]
Total	$ 1,100,000	$ 1,100,000
Secured Debt
Long-term Debt, Fiscal Year Maturity [Abstract]
2018	200,000
2019	600,000
2020	300,000
Total	1,100,000
Callable 2016	200,000
Callable 2017	$ 100,000
Secured Debt | Residential mortgage-backed securities
Long-term Debt, Fiscal Year Maturity [Abstract]
Composition of collateral that can be resold or repledged, as percentage	85.00%
Secured Debt | Obligations of GSEs
Long-term Debt, Fiscal Year Maturity [Abstract]
Composition of collateral that can be resold or repledged, as percentage	15.00%