Goodwill and Other Intangible Assets (Core Deposit Intangibles) (Details) - Core Deposit Intangibles - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Impairment write-downs on core deposit intangibles	$ 0	$ 0	$ 0
Gross balance	108,814,000	108,814,000
Accumulated amortization	(87,760,000)	(80,825,000)
Total	$ 21,054,000	$ 27,989,000