Loans and Allowance for Credit Losses Activity in the Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	$ 171,325	$ 171,412
Loans charged off	(9,407)	(11,155)
Recoveries of loans previously charged off	5,929	4,278
Net loans charged off	(3,478)	(6,877)
Provision for credit losses	4,800	1,530
Balance at end of period	$ 172,647	$ 166,065