Nature of business (Details) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2016 USD ($) segment $ / shares shares	Mar. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2015 $ / shares
Nature of business
Number of operating segments | segment	1
Numerator for earnings per common share calculation:
Net income | $	$ 2,700	$ 2,462
Denominator for earnings (loss) per common share calculation:
Weighted-average common shares, basic | shares	43,142	42,396
Effect of dilutive securities:
Stock options, restricted stock and warrants | shares	1,327	849
Weighted-average common shares, diluted | shares	44,469	43,245
EPS
Basic (in dollars per share) | $ / shares	$ 0.06	$ 0.06
Diluted (in dollars per share) | $ / shares	$ 0.06	$ 0.06
Shares excluded from the computation of diluted income (loss) per common share | shares	1,000
Common Class A
EPS
Par value of common stock (in dollars per share) | $ / shares	$ 0.0001		$ 0.0001
Common Class B
EPS
Par value of common stock (in dollars per share) | $ / shares	$ 0.0001		$ 0.0001