Repurchase Agreements Remaining Term to Maturity (Details) $ in Thousands	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Balance	$ 3,267,984	$ 2,565,902
WAVG Original Term to Maturity	66	54
Less than 30 days
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Balance	$ 2,319,911	$ 2,240,791
WAVG Original Term to Maturity	56	49
30 to 90 days
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Balance	$ 948,073	$ 274,231
WAVG Original Term to Maturity	89	90
Maturity Greater than 90 Days [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Balance	$ 0	$ 50,880
WAVG Original Term to Maturity	0	121