Summary of Unvested Restricted Stock Units (Detail) - Restricted Stock Units (RSUs) - shares		12 Months Ended
	Feb. 06, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Shares
Beginning Balance		419,000		37,000
Granted	80,000	2,351,000	907,000
Vested		(404,000)	(488,000)	(37,000)
Forfeited or cancelled		(577,000)
Ending Balance		1,789,000	419,000