Share-based Compensation - Share-based Compensation Plan - Option Activity (Detail) - Amended and Restated 2012 Long Term Incentive Plan [Member] - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Options
Options, outstanding beginning balance	4,406,752
Options, granted	1,093,100	854,800
Options, exercised	(164,499)
Options, canceled	(108,267)
Options, outstanding ending balance	5,227,086		4,406,752
Options, vested and expected to vest ending balance	5,093,258
Options, vested	2,215,513
Weighted Average Exercise Price
Weighted Average Exercise Price, outstanding beginning balance	$ 38.93
Weighted Average Exercise Price, granted	33.20
Weighted Average Exercise Price, exercised	26.74
Weighted Average Exercise Price, canceled	55.87
Weighted Average Exercise Price, outstanding ending balance	37.77		$ 38.93
Weighted Average Exercise Price, vested and expected to vest, ending balance	37.64
Weighted Average Exercise Price, vested	$ 29.37
Options, Additional Disclosures
Weighted Average Remaining Contractual Life, outstanding (in years)	8 years 25 days		7 years 7 months 6 days
Weighted Average Remaining Contractual Life, vested and expected to vest (in years)	8 years 10 days
Weighted Average Remaining Contractual Life, vested (in years)	6 years 8 months 4 days
Aggregate Intrinsic Value, outstanding	$ 30,991		$ 30,455
Aggregate Intrinsic Value, vested and expected to vest, ending balance	30,725
Aggregate Intrinsic Value, vested	$ 25,353