Revenue Recognition - Estimated Revenue Expected to be Recognized in Future Related to Performance Obligations (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transaction Price Allocated to the Remaining Performance Obligation as of March 31, 2019	$ 8,805
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | 2016 Agreement
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transaction Price Allocated to the Remaining Performance Obligation as of March 31, 2019	$ 1,525
Expected Year By Which Revenue Recognition Will Be Completed	2021
Percentage of Revenue Recognized	88.00%
Daiichi Sankyo, Inc ("Daiichi") | 2016 Agreement
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transaction Price Allocated to the Remaining Performance Obligation as of March 31, 2019	$ 3,257
Expected Year By Which Revenue Recognition Will Be Completed	2023
Percentage of Revenue Recognized	79.00%
Daiichi Sankyo, Inc ("Daiichi") | 2014 Agreement
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transaction Price Allocated to the Remaining Performance Obligation as of March 31, 2019	$ 1,112
Expected Year By Which Revenue Recognition Will Be Completed	2020
Percentage of Revenue Recognized	97.00%
Bayer Pharma AG | 2016 Agreement
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transaction Price Allocated to the Remaining Performance Obligation as of March 31, 2019	$ 2,911
Expected Year By Which Revenue Recognition Will Be Completed	2023
Percentage of Revenue Recognized	81.00%