Stock-Based Compensation - Schedule of Stock Option Activity (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share Based Compensation Stock Options Activity [Abstract]
Number of Shares, Outstanding, Beginning balance	3,822,887	2,584,554
Number of Shares, Options assumed through merger with SafeStitch		709,550
Number of Shares, Granted	2,422,309	603,139
Number of Shares, Forfeited	(670,065)	(6,129)
Number of Shares, Exercised	(151,390)	(68,227)
Number of Shares, Outstanding, Ending balance	5,423,741	3,822,887	2,584,554
Weighted Average Exercise Price, Outstanding	$ 1.30	$ 0.40
Weighted Average Exercise Price, Options assumed through merger with SafeStitch		$ 3.75
Weighted Average Exercise Price, Granted	$ 5.40	$ 2.20
Weighted Average Exercise Price, Forfeited	$ 3.95	$ 0.40
Weighted Average Exercise Price, Exercised	$ 0.49	$ 0.80
Weighted Average Exercise Price, Outstanding	$ 2.82	$ 1.30	$ 0.40
Weighted-Average Remaining Contractual Term (Years)	7 years 9 months 15 days	7 years 11 months 12 days	8 years 8 months 12 days