Allowance for Loan Losses - (Narrative) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($) loan
Allowance For Loan And Lease Losses [Line Items]
Provision (recoupment) for loan losses	$ 1,795	$ 10,619
Impaired loans	$ 25,500
Number of energy loans change in non-accrual	1
Impaired Energy Loans [Member]
Allowance For Loan And Lease Losses [Line Items]
Provision (recoupment) for loan losses		10,700
Impaired loans	$ 500
Non ASC 310-30 [Member]
Allowance For Loan And Lease Losses [Line Items]
Charge-offs, net	100	600
Provision (recoupment) for loan losses	1,800	11,481
Energy Specific Reserves		$ 9,100
Number of Energy Specific Reserves | loan		4
ASC 310-30 [Member]
Allowance For Loan And Lease Losses [Line Items]
Provision (recoupment) for loan losses	$ (5)	$ (862)