Loans and Allowance for Credit Losses Allowance for Credit Losses (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Receivables [Abstract]
Allowance for loan losses	$ 172,245	$ 172,342	$ 168,679	$ 162,526	$ 162,546	$ 169,054
Reserve for unfunded lending commitments	2,504		2,646
Allowance for credit losses	$ 174,749	$ 174,998	$ 171,325	$ 165,169	$ 165,108	$ 171,412