Repurchase Agreement Borrowings (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Dec. 31, 2015	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	$ 510,731	$ 554,242
Pledged Assets Separately Reported, Securities Pledged for Repurchase Agreements, at Fair Value	559,000	622,000
Available unpledged securities	536,000	585,000
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	7,300	9,800
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	209,627	247,618
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	0	2,239
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	0
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	$ 301,104	$ 304,385