Loans and Allowance for Credit Losses Activity in the Allowance for Credit Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Receivables [Abstract]
Balance at beginning of year	$ 171,325	$ 171,412	$ 185,931
Loans charged off	(33,290)	(33,927)	(32,157)
Recoveries of loans previously charged off	14,744	20,658	15,388
Net loans charged off	(18,546)	(13,269)	(16,769)
Provision for credit losses	23,305	13,182	2,250
Balance at end of year	$ 176,084	$ 171,325	$ 171,412