Income Taxes - Provision for Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Federal income taxes currently payable									$ 19,223	$ 22,908	$ 12,256
State income taxes currently payable									6,498	4,490	4,601
Federal income taxes deferred									3,188	20,402	(1,513)
State income taxes deferred									238	4,350	2,506
Deferred income tax expense									3,426	24,752	993
Income tax expense	$ 4,293	$ 12,154	$ 9,761	$ 2,939	$ 11,433	$ 13,254	$ 14,359	$ 13,104	$ 29,147	$ 52,150	$ 17,850