Restructuring Costs - Summary of Restructuring Activities (Detail) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Restructuring Cost and Reserve [Line Items]
Restructuring cost	$ 0		$ 0
Non-cash charges		$ (811,000)
Accrual, Ending balance		2,150,000
PNT2258 [Member]
Restructuring Cost and Reserve [Line Items]
Non-cash charges		(811,000)
Cash payments		(147,000)
Accrual, Ending balance		2,150,000
PNT2258 [Member] | Contract Termination [Member]
Restructuring Cost and Reserve [Line Items]
Non-cash charges		(681,000)
Cash payments		(18,000)
Accrual, Ending balance		2,093,000
PNT2258 [Member] | Employee Termination [Member]
Restructuring Cost and Reserve [Line Items]
Cash payments		(129,000)
Accrual, Ending balance		57,000
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		2,787,000
Research and development [Member] | PNT2258 [Member] | Contract Termination [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring cost		2,787,000
General and administrative [Member] | PNT2258 [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring cost		321,000
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		186,000
General and administrative [Member] | PNT2258 [Member] | Asset Impairment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring cost		$ 130,000