Acquisitions - Summary of Pre-tax Merger Related Costs (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Business Acquisition [Line Items]
Employee Expenses	$ 34,662,000	$ 26,908,000	$ 88,440,000	$ 79,755,000
Total Acquisition Related Expenses	13,016,000	$ 1,197,000	23,854,000	$ 1,197,000
Business Combinations, Legal and Professional Fees	0		6,542,000
Bank of the Cascades
Business Acquisition [Line Items]
Legal and Professional Fees	2,498,000		8,995,000
Employee Expenses	1,755,000		5,041,000
Technology Conversion and Contract Termination	7,090,000		7,779,000
Other	1,673,000		2,039,000
Total Acquisition Related Expenses	$ 13,016,000		$ 23,854,000