Income taxes - Provision (Benefit) for Income Taxes on Income from Continuing Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current
Federal	$ 77,795	$ 81,355	$ 155,558
State and other	9,527	7,981	5,792
Total	87,322	89,336	161,350
Deferred
Federal	15,765	(214,539)	(4,323)
State and other	4,280	(12,043)	(16,856)
Total	20,045	(226,582)	(21,179)
Total
Federal	93,560	(133,184)	151,235
State and other	13,807	(4,062)	(11,064)
Total	$ 107,367	$ (137,246)	$ 140,171