Loans - Impaired Loans Summary (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Impaired loans summary
Nonaccrual loans	$ 43,656,000		$ 43,656,000		$ 66,673,000
Accruing loans past due 90 days or more	4,828,000		4,828,000		1,169,000
Restructured loans - nonaccrual	10,555,000		10,555,000		10,133,000
Restructured loans - accruing	18,251,000		18,251,000		16,518,000
Total nonperforming loans	77,290,000		77,290,000		94,493,000
Impaired loans, other information
Total nonaccrual loans	54,200,000		54,200,000		76,800,000
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	1,000,000	$ 1,800,000	3,800,000	$ 3,400,000
Reserved based energy loans
Impaired loans, other information
Impaired Financing Receivable, with Related Allowance, Recorded Investment	12,100,000		12,100,000		14,000,000
Energy related service industry loans
Impaired loans, other information
Impaired Financing Receivable, with Related Allowance, Recorded Investment	34,300,000		34,300,000		42,200
Originated
Impaired loans summary
Nonaccrual loans	34,632,000		34,632,000		32,805,000
Accruing loans past due 90 days or more	1,069,000		1,069,000		1,169,000
Restructured loans - nonaccrual	7,755,000		7,755,000		6,959,000
Restructured loans - accruing	4,137,000		4,137,000		5,267,000
Total nonperforming loans	47,593,000		47,593,000		46,200,000
Impaired loans, other information
Impaired Financing Receivable, with Related Allowance, Recorded Investment	26,249,000		26,249,000		3,111,000
Acquired
Impaired loans summary
Nonaccrual loans	9,024,000		9,024,000		33,868,000
Accruing loans past due 90 days or more	3,759,000		3,759,000
Restructured loans - nonaccrual	2,800,000		2,800,000		3,174,000
Restructured loans - accruing	14,114,000		14,114,000		11,251,000
Total nonperforming loans	29,697,000		29,697,000		48,293,000
Impaired loans, other information
Impaired Financing Receivable, with Related Allowance, Recorded Investment	$ 22,000		$ 22,000		$ 1,755,000