Revenue Recognition - Estimated Revenue Expected to be Recognized in Future Related to Performance Obligations (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transaction Price Allocated to the Remaining Performance Obligation as of June 30, 2018	$ 14,494
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 June 30, 2018	$ 156
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 June 30, 2018	$ 2,383
Expected Year By Which Revenue Recognition Will Be Completed	2021
Percentage of Revenue Recognized	81.00%
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, 2018	$ 3,736
Expected Year By Which Revenue Recognition Will Be Completed	2020
Percentage of Revenue Recognized	89.00%
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, 2018	$ 4,212
Expected Year By Which Revenue Recognition Will Be Completed	2023
Percentage of Revenue Recognized	69.00%
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 June 30, 2018	$ 245
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 June 30, 2018	$ 3,762
Expected Year By Which Revenue Recognition Will Be Completed	2023
Percentage of Revenue Recognized	72.00%