Share-Based Compensation - Summary of Stock Option Activity (Detail)	9 Months Ended
	Sep. 30, 2018 $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Beginning balance of Outstanding, Options | shares	2,868,000
Granted, Options | shares	337,000
Exercised, Options | shares	(161,000)
Cancelled, Options | shares	(226,000)
Ending balance of Outstanding, Options | shares	2,818,000
Exercisable, Options | shares	1,828,000
Beginning balance of Outstanding, Weighted Average Exercise Price | $ / shares	$ 9.86
Granted, Weighted Average Exercise Price | $ / shares	14.10
Exercised, Weighted Average Exercise Price | $ / shares	8.46
Cancelled, Weighted Average Exercise Price | $ / shares	20.58
Ending balance of Outstanding, Weighted Average Exercise Price | $ / shares	9.59
Exercisable, Weighted Average Exercise Price | $ / shares	$ 10.17