Line of credit - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Debt Disclosure [Abstract]
Total availability under line of credit agreement	$ 10,000,000
Letters of credit outstanding amount	47,000
Varying Interest on Line of credit agreement	LIBOR plus 1.5% to Prime
Line of credit interest rate	1.50%
Maturity date of line of credit	Jun. 30, 2015
Line of credit facility amount outstanding	$ 0	$ 0
Maximum ratio of total liabilities to tangible net worth	11
Minimum required fixed coverage charge ratio	1.25
Period used for calculating ratios	12 months
Company's tangible net worth ratio	0.40
Fixed coverage charge ratio	2.86