Income Taxes - Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income taxes currently payable	$ 65,012	$ 29,354	$ 41,946
Deferred income taxes	(122)	34,911	8,412
Provision for income taxes	$ 64,890	$ 64,265	$ 50,358