Commitments and Contingencies - Additional Information (Details)	1 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended
	Dec. 31, 2014 USD ($) ft²	Dec. 31, 2013 USD ($) ft²	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) ft²
Commitments And Contingencies Disclosure [Abstract]
Lease period		3 years
Area of property leased | ft²	8,530	6,837					8,530
Monthly lease payments	$ 45,000	$ 31,000			$ 32,000
Rent abatement		$ 31,000
Lease commenced and rental payments period		2014-01
Cash-collateralized irrevocable standby letter of credit		$ 125,345	$ 125,345		$ 125,345
Lease space occupancy date	Mar. 13, 2015
Lease expiration date					Dec. 31, 2016
Landlord contribution for leasehold improvements	$ 100,000						$ 100,000
Additional cash security deposit paid to landlord	$ 179,130						179,130
Capital lease term					3 years
Capital lease commencement period					2014-02
Rent expense associated with lease			$ 200,000	$ 100,000	$ 300,000	$ 200,000
Contract cost incurred in research and development activities					$ 9,200,000		$ 4,300,000