Revenue Recognition - Estimated Revenue Expected to be Recognized in Future Related to Performance Obligations (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transaction Price Allocated to the Remaining Performance Obligation as of December 31, 2018	$ 10,491
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | 2014 Agreement
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transaction Price Allocated to the Remaining Performance Obligation as of December 31, 2018	$ 24
Expected Year By Which Revenue Recognition Will Be Completed	2019
Percentage of Revenue Recognized	99.00%
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 December 31, 2018	$ 1,832
Expected Year By Which Revenue Recognition Will Be Completed	2021
Percentage of Revenue Recognized	86.00%
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 December 31, 2018	$ 1,626
Expected Year By Which Revenue Recognition Will Be Completed	2020
Percentage of Revenue Recognized	95.00%
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 December 31, 2018	$ 3,681
Expected Year By Which Revenue Recognition Will Be Completed	2023
Percentage of Revenue Recognized	76.00%
Bayer Pharma, AG ('Bayer") and Janssen Pharmaceuticals, Inc. ("Janssen") | 2014 Agreement
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transaction Price Allocated to the Remaining Performance Obligation as of December 31, 2018	$ 37
Expected Year By Which Revenue Recognition Will Be Completed	2019
Percentage of Revenue Recognized	99.00%
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 December 31, 2018	$ 3,291
Expected Year By Which Revenue Recognition Will Be Completed	2023
Percentage of Revenue Recognized	79.00%