Derivatives and Hedging Activities (Narrative) (Details)	3 Months Ended
	Mar. 31, 2018 USD ($) counterparty instrument	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) instrument
Derivative [Line Items]
Gain (loss) on cash flow hedge ineffectiveness	$ 0	$ 0
Derivative instruments in accumulated other comprehensive income reclassified to interest expense	423,000
Derivative liability, notional amount	60,000,000
Derivative liabilities	$ 23,000
Dealer counterparties | counterparty	5
Dealer counterparty in liability position | counterparty	1
Derivatives Not Designated as a Hedging Instruments [Member] | Interest rate products [Member]
Derivative [Line Items]
Number of derivative instruments held (in instrument) | instrument	48		48
Derivative notional amount	$ 715,300,000		$ 718,500,000
Derivatives Not Designated as a Hedging Instruments [Member] | Credit contracts [Member]
Derivative [Line Items]
Number of derivative instruments held (in instrument) | instrument	2		2
Derivative notional amount	$ 15,800,000		$ 15,800,000
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Number of outstanding derivatives | instrument	2