Loans - Impaired Loans Summary (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Impaired loans summary
Nonaccrual loans	$ 66,628		$ 66,628		$ 37,541
Accruing loans past due 90 days or more	14,320		14,320		52
Restructured loans - nonaccrual	853		853		1,464
Restructured loans - accruing	5,469		5,469		5,988
Total nonperforming loans	87,270		87,270		45,045
Impaired loans, other infomation
Total nonaccrual loans	67,500		67,500		39,000
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	681	$ 66	1,600	$ 230
Reserved Based Energy Loans [Member]
Impaired loans, other infomation
Impaired Financing Receivable, with Related Allowance, Recorded Investment	46,200		46,200		32,300
Energy Related Service Industry Loans [Member]
Impaired loans, other infomation
Impaired Financing Receivable, with Related Allowance, Recorded Investment	$ 9,300		$ 9,300		$ 291