Commitments and Contingencies - Additional Information (Details)	1 Months Ended			3 Months Ended		6 Months Ended		12 Months Ended
	Nov. 30, 2015 USD ($) ft²	Dec. 31, 2014 USD ($) ft²	Dec. 31, 2013 USD ($) ft²	Jun. 30, 2016 USD ($) ft²	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) ft²	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Commitments And Contingencies [Line Items]
Lease period			3 years
Area of property leased | ft²		8,530	6,837
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
Lease space occupancy date		Mar. 13, 2015
Lease expiration date						Dec. 31, 2016
Landlord contribution for leasehold improvements		$ 100,000
Additional cash security deposit paid to landlord		$ 179,130
Rent expense associated with lease				$ 700,000	$ 200,000	$ 1,000,000	$ 400,000
Contract cost incurred in research and development activities						13,900,000		$ 5,200,000
Total remaining contract costs				443,200,000		$ 443,200,000
Office Equipment One
Commitments And Contingencies [Line Items]
Capital leases term						3 years
Capital lease commencement period						2014-02
Office Equipment Two
Commitments And Contingencies [Line Items]
Capital leases term						3 years
Capital lease commencement period						2015-04
Office Equipment Three
Commitments And Contingencies [Line Items]
Capital leases term						3 years
Capital lease commencement period						2016-02
Second Amendment
Commitments And Contingencies [Line Items]
Lease period						10 years
Area of property leased | ft²	23,189
Monthly lease payments	$ 107,000
Lease expiration date						Aug. 31, 2026
Additional cash security deposit paid to landlord	$ 976,382
Square feet of leased property | ft²	16,222
Operating lease payments commencement date						May 01, 2017
Second Amendment | Other Assets
Commitments And Contingencies [Line Items]
Additional cash security deposit paid to landlord				$ 1,280,857		$ 1,280,857		$ 304,475
Second Amendment | Delivered on December 31, 2015
Commitments And Contingencies [Line Items]
Monthly lease payments						$ 20,000
Square feet of leased property | ft²				3,066		3,066
Operating lease payments commencement date						Apr. 01, 2016
Second Amendment | Delivered on April 11, 2016
Commitments And Contingencies [Line Items]
Monthly lease payments						$ 110,000
Square feet of leased property | ft²				16,739		16,739
Operating lease payments commencement date						Sep. 11, 2016
Second Amendment | Delivered on January 1, 2017
Commitments And Contingencies [Line Items]
Monthly lease payments						$ 23,000
Square feet of leased property | ft²				3,384		3,384
Operating lease payments commencement date						May 01, 2017