Derivative Instruments and Balance Sheet Offsetting (Net Gains (Losses) Related to Changes in Fair Value) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative instruments
Net gains (losses) relating to derivative instruments	$ (1,431)	$ (83)	$ 61
Forward contracts related to mortgage loans to be delivered for sale | Net gain (loss) on sale of loans and other mortgage banking revenue
Derivative instruments
Net gains (losses) relating to derivative instruments	(669)	692	193
Interest rate lock commitments | Net gain (loss) on sale of loans and other mortgage banking revenue
Derivative instruments
Net gains (losses) relating to derivative instruments	266	(1,356)	(132)
Customer-initiated derivatives | Other noninterest income
Derivative instruments
Net gains (losses) relating to derivative instruments	$ (1,028)	$ 581	$ 0