Restructuring Costs - Summary of Restructuring Activities (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2017
Restructuring Cost and Reserve [Line Items]
Accrual, Beginning balance		$ 763
Accrual, Ending balance	$ 206	206
PNT2258 [Member]
Restructuring Cost and Reserve [Line Items]
Accrual, Beginning balance	495	763
Cash payments	(260)	(483)
Accrual, Ending balance	206	206
PNT2258 [Member] | Contract Termination [Member]
Restructuring Cost and Reserve [Line Items]
Accrual, Beginning balance	489	664
Cash payments	(256)	(386)
Accrual, Ending balance	204	204
PNT2258 [Member] | Employee Termination [Member]
Restructuring Cost and Reserve [Line Items]
Accrual, Beginning balance	6	99
Cash payments	(4)	(97)
Accrual, Ending balance	2	2
Research and development [Member] | PNT2258 [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring cost	(29)	(74)
Research and development [Member] | PNT2258 [Member] | Contract Termination [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring cost	$ (29)	$ (74)