Loans and Allowance for Credit Losses Activity in the Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	$ 174,998	$ 165,108	$ 171,325	$ 171,412
Loans charged off	(7,795)	(7,672)	(25,917)	(29,573)
Recoveries of loans previously charged off	2,471	3,592	12,766	15,148
Net loans charged off	(5,324)	(4,080)	(13,151)	(14,425)
Provision for credit losses	5,075	4,141	16,575	8,182
Balance at end of period	$ 174,749	$ 165,169	$ 174,749	$ 165,169