Repurchase Agreements Remaining Term to Maturity (Details) $ in Thousands	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Balance	$ 2,519,230	$ 2,898,952
WAVG Original Term to Maturity	53	63
Less than 30 days
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Balance	$ 1,725,518	$ 2,480,213
WAVG Original Term to Maturity	36	58
30 to 90 days
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Balance	$ 793,712	$ 418,739
WAVG Original Term to Maturity	89	87