Related party transactions - Additional Information (Detail) (Consulting Services [Member], USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Consulting Services [Member]
Related Party Transaction [Line Items]
Transaction expenses incurred by parent company	$ 40,000	$ 37,000	$ 71,000	$ 66,000
Outstanding payables due to related party	$ 24,000		$ 24,000		$ 12,000