Repurchase Agreements Remaining Term to Maturity (Details) $ in Thousands	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Balance	$ 2,514,984	$ 2,565,902
WAVG Original Term to Maturity	61	54
Less than 30 days
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Balance	$ 1,859,964	$ 2,240,791
WAVG Original Term to Maturity	49	49
30 to 90 days
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Balance	$ 635,668	$ 274,231
WAVG Original Term to Maturity	92	90
Maturity Greater than 90 Days [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Balance	$ 19,352	$ 50,880
WAVG Original Term to Maturity	178	121