Debt - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions						3 Months Ended				9 Months Ended	12 Months Ended
	Apr. 29, 2015	Dec. 19, 2014	Nov. 13, 2014	Nov. 15, 2013	Jun. 05, 2012	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013	Dec. 31, 2014	Mar. 31, 2013
Debt Instrument [Line Items]
Strike price per share	$ 9.41
Interest expense						$ 0.3		$ 0.5
Non-cash interest expense amortization of debt discount						$ 0.1		0.2
Debt Instrument, Maturity Date, Description						As part of the Hercules Second Amendment, this Minimum Threshold was amended to be the lower of $5.0 million or the aggregate outstanding principal balance of the Term Loans. As a result of the Company’s April 2015 equity offering, the Minimum Threshold was reduced to the lesser of $2.0 million or the aggregate outstanding principal balance of the Term Loans.
Senior Secured Loan
Debt Instrument [Line Items]
Number of shares received from warrants received to purchase common stock				25,641
Strike price per share			$ 17.00	$ 19.50
Senior Secured Loan | Hercules Technology Growth Capital
Debt Instrument [Line Items]
Number of shares received from warrants received to purchase common stock				25,641	13,927
Strike price per share				$ 19.50	$ 35.90
Fair value of warrants at issuance					$ 0.4
Debt, face amount				$ 10.0	10.0
Net proceeds from debt				9.8	$ 9.7
Interest rate on loan					11.00%
Interest expense						$ 1.0					$ 1.2
Non-cash interest expense amortization of debt discount								0.1
Legal and origination costs									$ 0.2
End of term fee						0.5
Total debt discount being amortized into interest expense						0.1		$ 0.1
Minimum amount of proceeds from specified asset dispositions for mandatory prepayment feature						1.0
Outstanding principal balance						5.7
Covenant, unrestricted cash balance requirement				$ 5.0		2.0
Repayments of term loan						2.0
Senior Secured Loan | Hercules Technology Growth Capital | Second Amendment
Debt Instrument [Line Items]
Number of shares received from warrants received to purchase common stock		58,823
Strike price per share		$ 11.00
Debt, face amount		$ 1.5
Net proceeds from debt		$ 1.4
Interest expense										$ 0.3
Legal and origination costs							$ 0.1
End of term fee										$ 0.1
Future raise in capital						10.0
Debt Instrument, Maturity Date										Jun. 01, 2017
Senior Secured Loan | Hercules Technology Growth Capital | Minimum
Debt Instrument [Line Items]
Prime rate					3.75%
Senior Secured Loan | Hercules Technology Growth Capital | Maximum | Second Amendment
Debt Instrument [Line Items]
Non-cash interest expense amortization of debt discount						$ 0.1