Repurchase Agreements Remaining Term to Maturity (Details) $ in Thousands	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Balance	$ 4,815,452	$ 3,267,984
WAVG Original Term to Maturity	62	66
Less than 30 days
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Balance	$ 4,175,623	$ 2,319,911
WAVG Original Term to Maturity	56	56
30 to 90 days
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Balance	$ 537,763	$ 948,073
WAVG Original Term to Maturity	90	89
91 to 180 days
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Balance	$ 102,066	$ 0
WAVG Original Term to Maturity	183	0