Collaboration and Licensing Agreements - Additional Information (Detail) $ in Thousands, $ in Millions, ¥ in Billions		1 Months Ended				3 Months Ended	9 Months Ended			12 Months Ended
	Nov. 02, 2018 USD ($)	Dec. 31, 2017 USD ($)		Nov. 30, 2017 USD ($)	Jun. 30, 2015 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2018 CAD ($)	Sep. 30, 2018 JPY (¥)	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)		Jan. 02, 2018 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Current assets		$ 149,712	[1]			$ 199,322			$ 199,322	$ 149,712	[1]	$ 5,000
Current liabilities		17,871	[1]			15,549			15,549	17,871	[1]	1,000
Revenues						172			2,522
Cost of revenue						2			466
Other
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues						172			202
Adjustments | ASU 2014-09
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Current assets						5,000			5,000			5,000
Current liabilities						1,000			1,000			1,000
Kyowa Hakko Kirin [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment received				$ 30,000
Kyowa Hakko Kirin [Member] | Product supply
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues						200			200
Kyowa Hakko Kirin [Member] | Adjustments | ASU 2014-09
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Current assets												5,000
Current liabilities												$ 1,000
Kyowa Hakko Kirin [Member] | Development and Commercialization [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development milestones									55,000
Commercialization milestones | ¥								¥ 8.5
Shanghai Fosun Pharmaceutical Industrial Development [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment received		$ 12,000
Revenues						0			0
Future development milestones	$ 113,000
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
AstraZeneca [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment received					$ 75,000
AstraZeneca [Member] | Development and Commercialization [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Cost of revenue									1,000
AstraZeneca [Member] | Termination Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Cost of revenue									500
Knight Therapeutics Inc [Member] | Development and Commercialization [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues						0			2,300
Total payments, including an up-front payment and development and sales milestones to be received							$ 25
Cost of revenue										$ 6,000
Knight Therapeutics Inc [Member] | Termination Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Cost of revenue					$ 9,900	$ 0			$ 500

[1] Derived from the audited consolidated financial statements included in the Company’s Annual Report on Form 10K for the year ended December 31, 2017.