Repurchase Agreement Borrowings (Details) (USD $)	3 Months Ended
	Mar. 31, 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	$ 539,961,000	$ 576,980,000
Pledged Assets Separately Reported, Securities Pledged for Repurchase Agreements, at Fair Value	581,000,000	664,000,000
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	234,438,000	268,427,000
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	26,000	164,000
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	1,878,000	4,940,000
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	303,619,000	303,449,000
Broker Repurchase Agreements [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Debt Instrument, Repurchase Amount			300,000,000
Long-term Debt, Prepayment Penalty	25,000,000
Payments of Debt Extinguishment Costs, Unamortized Balance	$ 13,600,000	$ 14,800,000