Restructuring Costs - Summary of Restructuring Activities (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Restructuring Cost and Reserve [Line Items]
Restructuring cost	$ 2,700,000	$ 0
Non-cash charges	(811,000)
Accrual, Ending balance	763,000
PNT2258 [Member]
Restructuring Cost and Reserve [Line Items]
Non-cash charges	(811,000)
Cash payments	(1,142,000)
Accrual, Ending balance	763,000
PNT2258 [Member] | Contract Termination [Member]
Restructuring Cost and Reserve [Line Items]
Non-cash charges	(681,000)
Cash payments	(909,000)
Accrual, Ending balance	664,000
PNT2258 [Member] | Employee Termination [Member]
Restructuring Cost and Reserve [Line Items]
Cash payments	(233,000)
Accrual, Ending balance	99,000
PNT2258 [Member] | Asset Impairment [Member]
Restructuring Cost and Reserve [Line Items]
Non-cash charges	(130,000)
Research and development [Member] | PNT2258 [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring cost	2,249,000
Research and development [Member] | PNT2258 [Member] | Contract Termination [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring cost	2,249,000
General and administrative [Member] | PNT2258 [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring cost	467,000
General and administrative [Member] | PNT2258 [Member] | Contract Termination [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring cost	5,000
General and administrative [Member] | PNT2258 [Member] | Employee Termination [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring cost	332,000
General and administrative [Member] | PNT2258 [Member] | Asset Impairment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring cost	$ 130,000