Income Tax Expense (Benefit) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Provision of Income Taxes [Line Items]
Current	$ 2,400	$ 77,700	$ 146,400
Deferred	(66,200)	109,400	48,800
Income taxes	(63,802)	187,141	195,173
Federal
Reconciliation of Provision of Income Taxes [Line Items]
Current	(41,300)	49,400	93,300
Deferred	(66,600)	109,600	49,200
Income taxes	(107,900)	159,000	142,500
State
Reconciliation of Provision of Income Taxes [Line Items]
Current	2,700	4,900	3,100
Deferred	600	300	(400)
Income taxes	3,300	5,200	2,700
Foreign
Reconciliation of Provision of Income Taxes [Line Items]
Current	41,000	23,400	50,000
Deferred	(200)	(500)
Income taxes	$ 40,800	$ 22,900	$ 50,000