Loans and Allowance for Credit Losses Non-Performing Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Receivables [Abstract]
Non-accrual loans	$ 124,749	$ 120,133
Loans 90 days or more past due and still accruing	10,010	11,505
Total non-performing loans	134,759	131,638
Other real estate owned	9,823	12,815
Total non-performing assets	$ 144,582	$ 144,453