Short and Long-Term Funding (Remaining Contractual Maturity of the Securities Sold Under Agreements to Repurchase) (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
RemainingContractualMaturityoftheSecuritiesSoldUnderAgreementtoRepurchase [Line Items]
Repurchase agreements	$ 214,869,000	$ 182,865,000
Overnight and Continuous
RemainingContractualMaturityoftheSecuritiesSoldUnderAgreementtoRepurchase [Line Items]
Repurchase agreements	214,869,000	182,865,000
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	214,869,000	182,865,000
Agency mortgage-related securities | Overnight and Continuous
RemainingContractualMaturityoftheSecuritiesSoldUnderAgreementtoRepurchase [Line Items]
Repurchase agreements	214,869,000	182,865,000
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