Related party transactions - Additional Information (Detail) (Consulting Services [Member], USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Consulting Services [Member]
Related Party Transaction [Line Items]
Transaction expenses incurred by parent company	$ 50,000	$ 59,000	$ 121,000	$ 125,000
Outstanding payables due to related party	$ 26,000		$ 26,000		$ 12,000