Equity - Summary of Stock Option Activity (Detail)	3 Months Ended
	Mar. 31, 2018 $ / shares shares
Number of shares
Stock options, beginning balance (in shares) | shares	6,342,526
Stock options, granted (in shares) | shares	1,720,500
Stock options, exercised (in shares) | shares	72,500
Stock options, canceled or expired (in shares) | shares	12,500
Stock options, ending balance (in shares) | shares	7,978,026
Stock options, exercisable, ending balance (in shares) | shares	2,250,840
Weighted average exercise price
Weighted average exercise price, beginning balance (in dollars per share) | $ / shares	$ 6.51
Weighted average exercise price, granted (in dollars per share) | $ / shares	8.06
Weighted average exercise price, exercised (in dollars per share) | $ / shares	4.14
Weighted average exercise price, canceled or expired (in dollars per share) | $ / shares	7.52
Weighted average exercise price, ending balance (in dollars per share) | $ / shares	6.86
Weighted average exercise price, exercisable, ending balance (in dollars per share) | $ / shares	$ 5.63