Collaboration and Licensing Agreements - Additional Information (Details) $ in Millions, ¥ in Billions		1 Months Ended					3 Months Ended			6 Months Ended			12 Months Ended
		Feb. 28, 2019 USD ($)	Mar. 31, 2018 CAD ($)	Dec. 31, 2017 USD ($)	Nov. 30, 2017 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 JPY (¥)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)		Dec. 31, 2017 USD ($)	Jan. 01, 2018 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Current assets							$ 127,241,000				$ 127,241,000		$ 176,371,000	[1]
Current liabilities							16,333,000				16,333,000		17,728,000	[1]
Unbilled license revenue	[1]												5,000,000
Revenues							18,000		$ 30,000		18,000	$ 2,350,000
Cost of revenue												464,000
Kyowa Hakko Kirin [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment received					$ 30,000,000
Unbilled license revenue							0				0
Revenues							18,000		30,000		18,000	30,000
Kyowa Hakko Kirin [Member] | Adjustments | ASU 2014-09
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Current assets																$ 5,000,000
Current liabilities																$ 1,000,000
Unbilled license revenue							0				0
Uncharged license fees reclassed to accounts payable								$ 1,000,000
Payment of uncharged license fee							1,000,000				1,000,000
Kyowa Hakko Kirin [Member] | Development and Commercialization [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development milestones											55,000,000
Development milestones Received											5,000,000
Commercialization milestones										¥ 8.5	78,700,000
Shanghai Fosun Pharmaceutical Industrial Development [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment received				$ 12,000,000
Revenues							0		0		0	0
Future development milestones															$ 113,000,000
Threshold percentage of net sales for tiered royalties				20.00%
Shanghai Fosun Pharmaceutical Industrial Development [Member] | Development and Commercialization [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Cost of revenue															2,400,000
AstraZeneca [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment received						$ 75,000,000
Payments of uncharged license fees							1,000,000
AstraZeneca [Member] | Development and Commercialization [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Cost of revenue		$ 1,000,000
Percentage of royalty revenue (as a percent)						10.00%
Percentage of non royalty revenue (as a percent)						20.00%
AstraZeneca [Member] | Termination Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Cost of revenue									0			500,000	$ 500,000
Knight | Development and Commercialization [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues							$ 0		$ 0		0	$ 2,300,000
Total payments, including an up-front payment and development and sales milestones to be received			$ 25								$ 19,100,000
Cost of revenue															$ 6,000,000
Knight | Termination Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Cost of revenue						$ 9,900,000

[1] Derived from the audited consolidated financial statements included in the Company’s Annual Report on Form 10K for the year ended December 31, 2018.