Income taxes - Provision (Benefit) for Income Taxes on Income from Continuing Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current
Federal	$ 81,355	$ 155,558	$ 72,291
State and other	7,981	5,792	3,984
Total	89,336	161,350	76,275
Deferred
Federal	(214,539)	(4,323)	47,547
State and other	(12,043)	(16,856)	(7,762)
Total	(226,582)	(21,179)	39,785
Total
Federal	(133,184)	151,235	119,838
State and other	(4,062)	(11,064)	(3,778)
Total	$ (137,246)	$ 140,171	$ 116,060