Loans and Allowance for Credit Losses Allowance for Credit Losses (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Receivables [Abstract]
Allowance for loan losses	$ 156,050	$ 163,217	$ 169,910	$ 172,342	$ 170,076	$ 168,679
Reserve for unfunded lending commitments	13,197		6,174
Allowance for credit losses	$ 169,247	$ 176,019	$ 176,084	$ 174,998	$ 172,647	$ 171,325