Income Taxes - Components of Net Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets:
Deferred compensation expense	$ 51,169	$ 86,327
Allowance for loan and lease losses and nonperforming assets	37,185	54,310
Investment securities	35,819	47,453
Deferred expense		435
State income taxes	5,155	14,293
Total deferred income tax assets before valuation allowance	129,328	202,818
Valuation allowance	(1,834)
Total deferred income tax assets after valuation allowance	127,494	202,818
Liabilities:
Leases	(13,634)	(39,397)
Deferred income	(6,262)
Intangible assets	(969)	(1,792)
Other	(8,130)	(9,793)
Total deferred income tax liabilities	(28,995)	(50,982)
Net deferred income tax assets	$ 98,499	$ 151,836