Summary of Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2018

Summary of Significant Accounting Policies [Abstract]

Impact of Adoption of Topic 606

Condensed Consolidated Balance Sheets

	December 31, 2017 (in thousands)
	As Revised Under Topic 606			As Originally Reported Under Topic 605			Effect of Change
Current portion of deferred revenue	$	58,192		$	50,579		$	7,613
Long‑term portion of deferred revenue		12,501			8,306			4,195
Accumulated deficit	$	(296,221	)	$	(284,413	)	$	(11,808	)

Condensed Consolidated Statements of Operations and Comprehensive Loss

	Three Months Ended June 30, 2017 (in thousands, except per share data)
	As Revised Under Topic 606			As Originally Reported Under Topic 605			Effect of Change
Research and development revenue under collaborative agreement	$	5,713		$	14,128		$	(8,415	)
Loss from operations		(19,689	)		(11,274	)		(8,415	)
Net loss		(20,359	)		(11,944	)		(8,415	)
Net loss per share of preferred stock, basic and diluted	$	(0.70	)	$	(0.41	)	$	(0.29	)

	Six Months Ended June 30, 2017 (in thousands, except per share data)
	As Revised Under Topic 606			As Originally Reported Under Topic 605			Effect of Change
Research and development revenue under collaborative agreement	$	11,807		$	23,725		$	(11,918	)
Loss from operations		(83,065	)		(71,147	)		(11,918	)
Net loss		(84,214	)		(72,296	)		(11,918	)
Net loss per share of preferred stock, basic and diluted	$	(2.92	)	$	(2.50	)	$	(0.42	)

Condensed Consolidated Statement of Cash Flows

	Six Months Ended June 30, 2017 (in thousands)
	As Revised Under Topic 606			As Originally Reported Under Topic 605			Effect of Change
Net loss	$	(84,214	)	$	(72,296	)	$	(11,918	)
Adjustments to reconcile net loss to net cash provided by operating activities:
Deferred revenue		63,193			51,275			11,918
Cash, cash equivalents and restricted cash at beginning of period		7,857			7,857			—
Cash, cash equivalents and restricted cash at end of period	$	75,445		$	75,445		$	—