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Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Collaborations, licenses and milestones	$ 10,941	$ 7,090	$ 13,340	$ 4,340	$ 6,440	$ 7,821	$ 66,007	$ 7,252	$ 35,711	$ 87,520	$ 27,762
Accounting Standard Update 2016 09 | Additional Paid-in Capital
Adoption of ASU 2016-09	400								400
Accounting Standard Update 2016 09 | Accumulated Deficit
Adoption of ASU 2016-09	$ (400)								(400)
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
Collaborations, licenses and milestones									$ 10,400	$ 21,500

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Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

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