Income taxes - Provision (Benefit) for Income Taxes on Income from Continuing Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current
Federal	$ 123,882	$ 59,791	$ 77,795
State and other	21,878	7,567	9,527
Total	145,760	67,358	87,322
Deferred
Federal	4,532	21,345	15,765
State and other	4,001	719	4,280
Total	8,533	22,064	20,045
Total
Federal	128,414	81,136	93,560
State and other	25,879	8,286	13,807
Total	$ 154,293	$ 89,422	$ 107,367