Repurchase Agreements Remaining Term to Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Balance	$ 4,872,869	$ 3,267,984
Assets Sold under Agreements to Repurchase, Interest Rate	2.32%	2.69%
WAVG Original Term to Maturity	45	66
Less than 30 days
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Balance	$ 2,751,900	$ 2,319,911
Assets Sold under Agreements to Repurchase, Interest Rate	2.39%	2.74%
WAVG Original Term to Maturity	37	56
30 to 90 days
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Balance	$ 2,120,969	$ 948,073
Assets Sold under Agreements to Repurchase, Interest Rate	2.22%	2.55%
WAVG Original Term to Maturity	55	89