Restructuring - Additional Information (Detail) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) Employee Employees
Restructuring Plan, July 2018 [Member]
Restructuring Cost and Reserve [Line Items]
Number of positions eliminated | Employee			30
Number of positions eliminated, period percent			53.00%
Restructuring charges		$ 7,400	$ 9,390
Payments for restructuring		1,689	5,756
Revised estimates during the year/ period		(1,945)	235
Restructuring Plan, July 2018 [Member] | One-time Employee Termination Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges			1,881
Payments for restructuring			1,881
Revised estimates during the year/ period			2
Restructuring Plan, July 2018 [Member] | Clinical Trial Closing [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges			5,744
Payments for restructuring		1,583	2,204
Revised estimates during the year/ period	$ 2,000	(1,957)	$ 41
Restructuring Plan, November 2018 [Member]
Restructuring Cost and Reserve [Line Items]
Number of positions eliminated | Employees			16
Restructuring Plan, November 2018 [Member] | One-time Employee Termination Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges		1,645	$ 984
Restructuring charges and related cost, incurred cost		700
Payments for restructuring		702	922
Research and Development Expenses [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges			9,000
Restructuring recoveries		1,900
General and Administrative Expenses [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 700	1,100
Miscellaneous Expenses [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges			$ 300