Income Taxes - Loss from Continuing Operations Before Benefit for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Benefit for income taxes at federal statutory rate	$ (24,868)	$ (45,531)	$ (27,512)
State current and deferred income tax benefit	(2,699)	(4,452)	(2,184)
Energy credit		(888)	(2,846)
Valuation allowance	7,651	11,855	918
Tax reform	(22,988)
Other	2,145	(2,940)	(896)
Benefit for income taxes	$ (40,759)	$ (41,956)	$ (32,520)