Loans - Other (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Loans and Leases Receivable, Other Information [Abstract]
Net deferred loan origination fees and unamortized premium and discount	$ 13,400,000	$ 17,400,000
Non-accretable discount on acquired credit impaired loans	1,800,000	3,000,000
Accrued interest receivable on loans	$ 7,900,000	$ 7,400,000
Concentration risk	0.00%	0.00%
Consumer and other
Loans and Leases Receivable, Other Information [Abstract]
Deposit Liabilities Reclassified as Loans Receivable	$ 41,000	$ 73,000
Reserved based energy loans
Loans and Leases Receivable, Other Information [Abstract]
Percentage of total funded loans	0.40%	0.50%
Loans	$ 12,100,000	$ 14,000,000
Energy related service industry loans
Loans and Leases Receivable, Other Information [Abstract]
Percentage of total funded loans	1.90%	2.60%
Loans	$ 34,300,000	$ 42,200