Acquisitions - Schedule of Acquisition Related Expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Salaries and wages	$ 122,751	$ 108,684	$ 101,451
Total acquisition related expenses	27,156	$ 2,821	$ 795
Cascade Bank
Business Acquisition [Line Items]
Legal and professional fees	9,600
Salaries and wages	5,100
Technology conversion and contract termination	10,200
Other	2,300
Total acquisition related expenses	$ 27,200