Summary of Significant Accounting Policies - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2015 USD ($) Segment	Dec. 31, 2014 USD ($)
Summary Of Significant Accounting Policy [Line Items]
Deferred offering costs	$ 3,053,000	$ 549,000
Number of operating segment | Segment	1
Leasehold Improvements [Member]
Summary Of Significant Accounting Policy [Line Items]
Estimated useful lives of assets	3 years
Minimum [Member]
Summary Of Significant Accounting Policy [Line Items]
Estimated useful lives of assets	3 years
Maximum [Member]
Summary Of Significant Accounting Policy [Line Items]
Estimated useful lives of assets	5 years
Other Noncurrent Assets [Member]
Summary Of Significant Accounting Policy [Line Items]
Long-term portion of restricted cash	$ 200,000
Prepaid Expenses and Other Current Assets [Member]
Summary Of Significant Accounting Policy [Line Items]
Current portion of restricted cash	$ 25,000