Restructuring Costs - Summary of Restructuring Activities (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Restructuring Cost and Reserve [Line Items]
Non-cash charges			$ (811,000)
Restructuring cost		$ 0		$ 0
Accrual, Ending balance	$ 1,475,000		1,475,000
PNT2258 [Member]
Restructuring Cost and Reserve [Line Items]
Accrual, Beginning balance	2,150,000
Non-cash charges			(811,000)
Cash payments	(355,000)		(502,000)
Accrual, Ending balance	1,475,000		1,475,000
PNT2258 [Member] | Contract Termination [Member]
Restructuring Cost and Reserve [Line Items]
Accrual, Beginning balance	2,093,000
Non-cash charges			(681,000)
Cash payments	(254,000)		(272,000)
Accrual, Ending balance	1,419,000		1,419,000
PNT2258 [Member] | Employee Termination [Member]
Restructuring Cost and Reserve [Line Items]
Accrual, Beginning balance	57,000
Cash payments	(101,000)		(230,000)
Accrual, Ending balance	56,000		56,000
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	(420,000)		2,367,000
Research and development [Member] | PNT2258 [Member] | Contract Termination [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring cost	(420,000)		2,367,000
General and administrative [Member] | PNT2258 [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring cost	100,000		421,000
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	$ 100,000		286,000
General and administrative [Member] | PNT2258 [Member] | Asset Impairment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring cost			$ 130,000