Income Taxes - Components of Net Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets:
Deferred compensation expense	$ 57,727	$ 56,148
Allowance for credit losses and nonperforming assets	63,899	35,195
Lease liabilities	10,839	11,951
Investment securities		2,474
State income taxes	4,243	3,338
Total deferred income tax assets before valuation allowance	136,708	109,106
Valuation allowance	(1,675)	(1,393)
Total deferred income tax assets after valuation allowance	135,033	107,713
Liabilities:
Leases	(18,583)	(14,873)
Investment securities	(19,965)
Deferred income	(11,399)	(16,069)
Lease right-of-use assets	(10,736)	(11,931)
Intangible assets	(604)	(500)
Other	(19,222)	(10,570)
Total deferred income tax liabilities	(80,509)	(53,943)
Net deferred income tax assets	$ 54,524	$ 53,770