Allowance for Loan Losses - (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Allowance For Loan And Lease Losses [Line Items]
Provision (recoupment) for loan losses	$ 23,651	$ 12,444	$ 6,209
Non ASC 310-30 [Member]
Allowance For Loan And Lease Losses [Line Items]
Charge-offs, net	21,600	2,900
Provision (recoupment) for loan losses	24,456	12,078
Non ASC 310-30 [Member] | Energy Loans [Member]
Allowance For Loan And Lease Losses [Line Items]
Charge-offs, net	19,100
Provision (recoupment) for loan losses	18,900
ASC 310-30 [Member]
Allowance For Loan And Lease Losses [Line Items]
Provision (recoupment) for loan losses	(805)	366
ASC 310-30 [Member] | Commercial Portfolio Segment [Member]
Allowance For Loan And Lease Losses [Line Items]
Provision (recoupment) for loan losses	$ (788)	$ 320