Organization and Operations - Additional Information (Detail) $ in Thousands		1 Months Ended			12 Months Ended
	Jan. 04, 2018	Aug. 31, 2016 USD ($)	Aug. 31, 2015 USD ($)	Feb. 28, 2015 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2017 USD ($)
Schedule Of Description Of Business [Line Items]
Net proceeds from issuance of common stock and convertible senior notes				$ 55,398
Proceeds from the issuance of common stock			$ 73,965
Net proceeds from second offering of convertible senior notes		$ 48,738			$ 3,997
Accumulated deficit					$ (238,877)	$ (268,374)
Aggregate cash and cash equivalents and marketable securities						$ 100,014
Subsequent Events [Member]
Schedule Of Description Of Business [Line Items]
Reverse stock split, conversion ratio	0.25
Subsequent Events [Member] | Inotek [Member]
Schedule Of Description Of Business [Line Items]
Reverse stock split, description	1-for-4 reverse stock split
Reverse stock split, conversion ratio	0.25
Number of common stock converted for each outstanding share under merger agreement	76.185