Collaboration and Licensing Agreements - Additional Information (Details) - USD ($)		1 Months Ended		3 Months Ended
	Jan. 27, 2017	May 31, 2017	Feb. 28, 2017	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Jan. 01, 2018	Mar. 31, 2017
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Receivables from collaborations				$ 2,513,000		$ 1,997,000
Mars, Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential license agreement fee				23,600,000
Additional potential payments based on sale of first licensed product				95,000,000
License fee				0	$ 0
Incyte Collaboration Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of sharing in global development cost	30.00%
Future profits and losses share percentage	40.00%
Upfront payment received			$ 45,000,000
Development milestone achieved								$ 12,000,000
Development milestone received		$ 12,000,000
Additional potential development, regulatory and sales milestones receivable				$ 418,000,000
Future net profits and losses share percentage				40.00%
Profit and loss sharing description				Incyte and the Company will share in any future United States net profits and losses, with the Company bearing 40% and Incyte bearing 60%, respectively, and outside the United States the Company will be eligible to receive from Incyte tiered royalties, with rates in the low to mid-teens of sales.
Upfront consideration allocated to combined unit of accounting				$ 45,000,000
Development milestone recognized				12,000,000
Reduction of research and development expenses				800,000	1,100,000
Receivables from collaborations				2,500,000		$ 2,000,000
Incyte Collaboration Agreement | ASC 606
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration agreement transaction price							$ 57,000,000
Collaboration revenue recognized related to completion of combined performance obligation				$ 0	$ 5,200,000
Incyte Collaboration Agreement | Opt Out of Co-Funding Obligations
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Additional potential development, regulatory and commercialization milestones receivable	$ 738,000,000
Incremental royalty percentage on annual net sales	3.00%
Maximum incremental royalty, percentage of previous development expenditure	120.00%
Incyte Collaboration Agreement | Incyte
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of sharing in global development cost	70.00%
Future profits and losses share percentage	60.00%
Future net profits and losses share percentage				60.00%