Loans and Allowance for Credit Losses Non-Performing Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Receivables [Abstract]
Non-accrual loans	$ 122,966	$ 124,749
Loans 90 days or more past due and still accruing	11,676	10,010
Total non-performing loans	134,642	134,759
Other real estate owned (OREO)	10,744	9,823
Total non-performing assets	$ 145,386	$ 144,582