Income Taxes - Income Tax Expense Benefit Income Tax Reconciliation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Tax benefit at statutory rate	$ (45,272)	$ (44,788)	$ (420,544)
Tax effect of:
Effect of the Tax Cuts and Jobs Act net of valuation allowance	(19,086)
Valuation allowance on deferred tax assets	41,116	69,890	283,585
State income taxes, net of federal benefit	(892)	(18,860)	(18,218)
Nondeductible stock-based compensation	1,408	73	539
Net operating loss expirations	1,548
Other	3,234	854	193
Total	$ (17,944)	$ 7,169	$ (154,445)