Income Taxes - Reconciliation of Total Income Tax Expense (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Computed income tax expense at statutory rate									$ 44,389	$ 64,050	$ 34,410
Effects of tax reform									(284)	19,022
Tax exempt interest, net									(1,609)	(3,988)	(2,744)
BOLI income									(717)	(1,148)	(1,023)
State tax expense									3,527	2,279	1,760
Goodwill writeoff on sale of subsidiary assets									2,254
One-time bad debt deduction on legacy loan portfolio									(5,565)
Other, net									3,122	431	137
Total income tax expense	$ 10,709	$ 15,074	$ 8,384	$ 10,950	$ 36,980	$ 17,457	$ 13,570	$ 12,639	$ 45,117	$ 80,646	$ 32,540