Summary of Significant Accounting Policies - Additional Information (Details)	3 Months Ended			6 Months Ended
	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Mar. 25, 2014 USD ($) shares	Jun. 30, 2015 USD ($) Segment	Jun. 30, 2014 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Accretion on preferred stock			$ 86,900,000		$ 86,900,000
Number of operating segments | Segment				1
Revenue				$ 0
Expected dividend yield				0.00%
Depreciation expense				$ 50,000	20,000
Assets Held under Capital Leases
Summary Of Significant Accounting Policies [Line Items]
Depreciation expense	$ 32,000	$ 12,000		$ 50,000	$ 20,000
Minimum
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, Useful life				3 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, Useful life				7 years
IPO
Summary Of Significant Accounting Policies [Line Items]
Convertible redeemable preferred stock converted into common stock | shares			12,115,183