Repurchase Agreement Borrowings (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Dec. 31, 2014	Nov. 30, 2012
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount	$ 538,618	$ 576,980
Pledged Assets Separately Reported, Securities Pledged for Repurchase Agreements, at Fair Value	588,000	664,000
Available unpledged securities	348,000	347,000
Long-term Debt [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Long-term Debt, Prepayment Penalty	25,000
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount			$ 300,000
Payments of Debt Extinguishment Costs, Unamortized Balance	12,400	14,800
Maturity Overnight [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount	231,359	268,427
Maturity up to 30 days [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount	2,035	164
Maturity 30 to 90 Days [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount	0	4,940
Maturity over 90 days [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount	$ 305,224	$ 303,449