Summary of Stock Options Issued Pursuant to Stock Incentive Plans (Detail)	3 Months Ended
	Mar. 31, 2016 USD ($) $ / shares shares
Number of Shares
Outstanding, Beginning Balance | shares	5,799,076
Granted | shares	2,284,500
Exercised | shares	(15,885)
Forfeited | shares	(86,680)
Outstanding, Ending Balance | shares	7,981,011
Number of Shares Exercisable, Ending Balance | shares	4,254,017
Weighted-Average Exercise Price
Beginning Balance | $ / shares	$ 14.37
Granted | $ / shares	17.92
Exercised | $ / shares	11.14
Forfeited | $ / shares	19.10
Ending Balance | $ / shares	15.34
Weighted-Average Exercise Price Exercisable, Ending Balance | $ / shares	$ 12.59
Weighted-Average Remaining Contractual Term (Years)
Weighted Average Remaining Contractual Term (Years), Outstanding as of end of period	7 years 26 days
Weighted-Average Remaining Contractual Term (Years), Exercisable as of end of period	5 years 11 days
Aggregate Intrinsic Value of In-the-Money Options
Aggregate Intrinsic Value of In-the-Money Options, Outstanding as of end of period | $	$ 43,551,458
Aggregate Intrinsic Value of In-the-Money Options, Exercisable as of end of period | $	$ 34,890,634