Income Taxes - Components of income tax expense (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current
Current federal income tax expense (benefit)									$ 31,969	$ 35,401	$ 64,910
Current state income tax expense (benefit)									21,806	27,749	24,739
Current income tax expense (benefit)									53,775	63,150	89,649
Deferred
Deferred federal income tax expense (benefit)									874	2,336	31,464
Deferred state income tax expense (benefit)									661	406	3,276
Deferred income tax expense (benefit)									1,535	2,742	34,740
Total
Federal income tax expense (benefit)									32,843	37,737	96,374
State income tax expense (benefit)									22,467	28,155	28,015
Income tax provision	$ 12,049	$ 14,566	$ 14,256	$ 14,439	$ 16,069	$ 15,461	$ 16,629	$ 17,733	$ 55,310	$ 65,892	$ 124,389