Employee benefit plans - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Compensation And Retirement Disclosure [Abstract]
Non-qualified deferred compensation plan allowable eligible participants deferral percentage of base salary			80.00%
Non-qualified deferred compensation plan allowable eligible participants deferral percentage of other compensation			100.00%
Employee deferrals deemed vested percentage upon contribution			100.00%
Company's contributions to the plan	$ 200,000	$ 200,000	$ 400,000	$ 300,000
Company's expected contributions to the plan	$ 6,000	$ 0	$ 15,000	$ 0