Revenue from Contracts with Customers Schedule of Impact of Changes in Accounting Standard (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue									$ 106,732	$ 114,905	$ 86,489
Net loss	$ (21,111)	$ (16,486)	$ (20,601)	$ (19,202)	$ (8,751)	$ (11,404)	$ (4,555)	$ (18,852)	$ (77,400)	$ (43,562)	$ (47,089)
Net loss per share - basic and diluted (in dollars per share)	$ (0.68)	$ (0.56)	$ (0.80)	$ (0.75)	$ (0.34)	$ (0.45)	$ (0.20)	$ (0.87)	$ (2.78)	$ (1.84)	$ (2.34)
Deferred revenue, current portion	$ 9,890				$ 9,229				$ 9,890	$ 9,229
Accumulated deficit	$ (391,256)				$ (313,102)				(391,256)	(313,102)
Calculated under Revenue Guidance in Effect before Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue									105,978
Net loss									$ (78,154)
Net loss per share - basic and diluted (in dollars per share)									$ (2.80)
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue									$ 754
Net loss									$ 754
Net loss per share - basic and diluted (in dollars per share)									$ 0.02
Product And Service
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue									$ 83,523	72,010	$ 69,134
Product And Service | Calculated under Revenue Guidance in Effect before Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue									82,769
Product And Service | Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue									(754)
Collaboration
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue									23,209	$ 42,895	$ 17,355
Collaboration | Calculated under Revenue Guidance in Effect before Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue									23,209
Collaboration | Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue									$ 0