Stock-Based Compensation - Schedule of Unvested Stock Option Activity (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Granted	2,422,309	603,139
Unvested Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Beginning balance	1,816,566	1,707,536
Number of Shares, Unvested options assumed through merger with SafeStitch		223,200
Number of Shares, Granted	2,422,309	603,139
Number of Shares, Vested	(993,888)	(711,818)
Number of Shares, Forfeited	(542,410)	(5,490)
Number of Shares, Ending balance	2,702,577	1,816,566
Weighted-Average Fair Value, Beginning balance	1.10	0.40
Weighted-Average Fair Value, Unvested options assumed through merger with SafeStitch		2.45
Weighted-Average Fair Value, Granted	2.87	0.95
Weighted-Average Fair Value, Vested	1.04	1.25
Weighted-Average Fair Value, Forfeited	2.25	0.20
Weighted-Average Fair Value, Ending balance	2.33	1.10