Repurchase Agreements Remaining Term to Maturity (Details) $ in Thousands	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Balance	$ 4,252,893	$ 3,267,984
WAVG Original Term to Maturity	58	66
Less than 30 days
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Balance	$ 3,459,566	$ 2,319,911
WAVG Original Term to Maturity	52	56
30 to 90 days
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Balance	$ 793,327	$ 948,073
WAVG Original Term to Maturity	82	89