Income Taxes - Income Tax Expense (Benefit) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Components Of Income Tax Expense Benefit Continuing Operations [Abstract]
Income tax expense (benefit)	$ 57,651	$ (129,488)	$ 170,046	$ (171,464)
Effective tax rate	45.30%	36.50%	41.50%	35.00%