Loans - Impaired Loans Summary (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Impaired loans summary
Nonaccrual loans	$ 84,491		$ 84,491		$ 37,541
Accruing loans past due 90 days or more	3,664		3,664		52
Restructured loans - nonaccrual	8,961		8,961		1,464
Restructured loans - accruing	5,378		5,378		5,988
Total nonperforming loans	102,494		102,494		45,045
Impaired loans, other infomation
Total nonaccrual loans	93,500		93,500		39,000
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	1,800	$ 83	3,400	$ 313
Reserved Based Energy Loans [Member]
Impaired loans, other infomation
Impaired Financing Receivable, with Related Allowance, Recorded Investment	25,800		25,800		32,300
Energy Related Service Industry Loans [Member]
Impaired loans, other infomation
Impaired Financing Receivable, with Related Allowance, Recorded Investment	38,000		38,000		291
Originated [Member]
Impaired loans summary
Nonaccrual loans	52,005		52,005		35,145
Accruing loans past due 90 days or more	1,082		1,082		45
Restructured loans - nonaccrual	8,695		8,695		558
Restructured loans - accruing	5,368		5,368		5,694
Total nonperforming loans	67,150		67,150		41,442
Impaired loans, other infomation
Impaired Financing Receivable, with Related Allowance, Recorded Investment	41,580		41,580		32,689
Acquired [Member]
Impaired loans summary
Nonaccrual loans	32,486		32,486		2,396
Accruing loans past due 90 days or more	2,582		2,582		7
Restructured loans - nonaccrual	266		266		906
Restructured loans - accruing	10		10		294
Total nonperforming loans	35,344		35,344		3,603
Impaired loans, other infomation
Impaired Financing Receivable, with Related Allowance, Recorded Investment	$ 16,464		$ 16,464		$ 52