Loans and Allowance for Credit Losses Activity in the Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	$ 172,647	$ 166,065	$ 171,325	$ 171,412
Loans charged off	(8,715)	(10,746)	(18,122)	(21,901)
Recoveries of loans previously charged off	4,366	7,278	10,295	11,556
Net loans charged off	(4,349)	(3,468)	(7,827)	(10,345)
Provision for credit losses	6,700	2,511	11,500	4,041
Balance at end of period	$ 174,998	$ 165,108	$ 174,998	$ 165,108