Equity - Summary of Stock Option Activity (Detail)	9 Months Ended
	Sep. 30, 2018 $ / shares shares
Number of shares
Stock options, beginning balance (in shares) | shares	6,342,526
Stock options, granted (in shares) | shares	2,172,102
Stock options, exercised (in shares) | shares	1,094,324
Stock options, canceled or expired (in shares) | shares	338,250
Stock options, ending balance (in shares) | shares	7,082,054
Stock options, exercisable, ending balance (in shares) | shares	2,965,695
Weighted average price
Weighted average exercise price, beginning balance (in dollars per share) | $ / shares	$ 6.51
Weighted average exercise price, granted (in dollars per share) | $ / shares	8.42
Weighted average exercise price, exercised (in dollars per share) | $ / shares	5.60
Weighted average exercise price, canceled or expired (in dollars per share) | $ / shares	7.03
Weighted average exercise price, ending balance (in dollars per share) | $ / shares	7.21
Weighted average exercise price, exercisable, ending balance (in dollars per share) | $ / shares	$ 6.20