Derivative Instruments (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Derivative [Line Items]
Derivative, fair value	$ 4,000,000		$ 4,300,000
Loss on sale of outstanding commitments	735,000	$ (2,500,000)
Collateral requirements	32,700,000		43,800,000
Variation margin, amount reducing derivative asset	8,100,000		1,500,000
Fixed Rate Residential Mortgage
Derivative [Line Items]
Commitments to fund fixed-rate mortgage loans	93,100,000		49,300,000
Unrealized gain (loss) on fair value of fixed-rate mortgage loans to customers	(192,000)	$ 674,000
Sale of outstanding commitments	113,000,000		72,500,000
Interest Rate Swap
Derivative [Line Items]
Notional amount of interest rate swap contracts	1,550,000,000
Increase in derivative, notional amount	$ 82,000,000
Cash Flow Hedges
Derivative [Line Items]
Derivative instruments			0
Fair Value Hedges
Derivative [Line Items]
Derivative instruments			$ 0