Short and Long-Term Funding (Remaining Contractual Maturity of the Securities Sold Under Agreements to Repurchase) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
RemainingContractualMaturityoftheSecuritiesSoldUnderAgreementtoRepurchase [Line Items]
Repurchase agreements	$ 326,823	$ 300,197
Overnight and Continuous
RemainingContractualMaturityoftheSecuritiesSoldUnderAgreementtoRepurchase [Line Items]
Repurchase agreements	326,823	300,197
Up to 30 days
RemainingContractualMaturityoftheSecuritiesSoldUnderAgreementtoRepurchase [Line Items]
Repurchase agreements	0	0
30-90 days
RemainingContractualMaturityoftheSecuritiesSoldUnderAgreementtoRepurchase [Line Items]
Repurchase agreements	0	0
Greater than 90 days
RemainingContractualMaturityoftheSecuritiesSoldUnderAgreementtoRepurchase [Line Items]
Repurchase agreements	0	0
Agency mortgage-related securities
RemainingContractualMaturityoftheSecuritiesSoldUnderAgreementtoRepurchase [Line Items]
Repurchase agreements	326,823	300,197
Agency mortgage-related securities | Overnight and Continuous
RemainingContractualMaturityoftheSecuritiesSoldUnderAgreementtoRepurchase [Line Items]
Repurchase agreements	326,823	300,197
Agency mortgage-related securities | Up to 30 days
RemainingContractualMaturityoftheSecuritiesSoldUnderAgreementtoRepurchase [Line Items]
Repurchase agreements	0	0
Agency mortgage-related securities | 30-90 days
RemainingContractualMaturityoftheSecuritiesSoldUnderAgreementtoRepurchase [Line Items]
Repurchase agreements	0	0
Agency mortgage-related securities | Greater than 90 days
RemainingContractualMaturityoftheSecuritiesSoldUnderAgreementtoRepurchase [Line Items]
Repurchase agreements	$ 0	$ 0