Organization and Basis of Presentation - Additional Information (Detail) (USD $)	3 Months Ended		12 Months Ended	0 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Apr. 17, 2015	Dec. 02, 2014	Feb. 11, 2014	Nov. 30, 2014
Organization And Basis Of Presentation [Line Items]
Collaboration and license agreement, date	May 28, 2013
Accumulated deficit	$ (98,274,000)		$ (91,750,000)
Proceeds from issuance of common stock	(46,000)	51,507,000
Silicon Valley Bank [Member]
Organization And Basis Of Presentation [Line Items]
Maximum borrowing capacity							15,000,000
Amount borrowed			10,000,000
Subsequent Event [Member]
Organization And Basis Of Presentation [Line Items]
Issuance of common stock				1,251,784
Proceeds from issuance of common stock				12,500,000
Initial Public Offering ("IPO") [Member]
Organization And Basis Of Presentation [Line Items]
Issuance of common stock					1,743,680	5,750,000
Proceeds from issuance of common stock					18,200,000	50,200,000
Issuance of warrants					871,840
Initial Public Offering ("IPO") [Member] | Subsequent Event [Member]
Organization And Basis Of Presentation [Line Items]
Issuance of common stock				1,251,784
Proceeds from issuance of common stock				$ 12,500,000