Loans - Impaired Loans Summary (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Impaired loans summary
Nonaccrual loans	$ 43,257,000		$ 43,257,000		$ 66,673,000
Accruing loans past due 90 days or more	2,651,000		2,651,000		1,169,000
Restructured loans - nonaccrual	19,362,000		19,362,000		10,133,000
Restructured loans - accruing	7,637,000		7,637,000		16,518,000
Total nonperforming loans	72,907,000		72,907,000		94,493,000
Impaired loans, other information
Total nonaccrual loans	62,600,000		62,600,000		76,800,000
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	1,100,000	$ 681,000	2,800,000	$ 1,600,000
Reserved based energy loans
Impaired loans, other information
Impaired Financing Receivable, with Related Allowance, Recorded Investment	12,200,000		12,200,000		14,000,000
Energy related service industry loans
Impaired loans, other information
Impaired Financing Receivable, with Related Allowance, Recorded Investment	32,300,000		32,300,000		42,200
Originated
Impaired loans summary
Nonaccrual loans	33,755,000		33,755,000		32,805,000
Accruing loans past due 90 days or more	959,000		959,000		1,169,000
Restructured loans - nonaccrual	8,225,000		8,225,000		6,959,000
Restructured loans - accruing	4,204,000		4,204,000		5,267,000
Total nonperforming loans	47,143,000		47,143,000		46,200,000
Impaired loans, other information
Impaired Financing Receivable, with Related Allowance, Recorded Investment	21,056,000		21,056,000		3,111,000
Acquired
Impaired loans summary
Nonaccrual loans	9,502,000		9,502,000		33,868,000
Accruing loans past due 90 days or more	1,692,000		1,692,000
Restructured loans - nonaccrual	11,137,000		11,137,000		3,174,000
Restructured loans - accruing	3,433,000		3,433,000		11,251,000
Total nonperforming loans	25,764,000		25,764,000		48,293,000
Impaired loans, other information
Impaired Financing Receivable, with Related Allowance, Recorded Investment	$ 5,209,000		$ 5,209,000		$ 1,755,000