Revenue Recognition - Estimated Revenue Expected to be Recognized in Future Related to Performance Obligations (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transaction Price Allocated to the Remaining Performance Obligation as of June 30, 2019	$ 7,405
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 June 30, 2019	$ 856
Expected Year By Which Revenue Recognition Will Be Completed	2021
Percentage of Revenue Recognized	93.00%
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 June 30, 2019	$ 3,120
Expected Year By Which Revenue Recognition Will Be Completed	2023
Percentage of Revenue Recognized	80.00%
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 June 30, 2019	$ 942
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 June 30, 2019	$ 2,487
Expected Year By Which Revenue Recognition Will Be Completed	2023
Percentage of Revenue Recognized	84.00%