Stock based compensation - Restricted Stock - (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Restricted stock disclosures
Stock-based compensation	$ 4,040	$ 3,518
Restricted stock units
Shares
Balance, beginning (in shares)	455,404
Granted (in shares)	429,103
Vested (in shares)	(108,600)
Forfeited (in shares)	(28,480)
Balance, ending (in shares)	747,427
Weighted Average Grant Date Fair Value Per Share
Balance, beginning (in dollars per share)	$ 12.16
Issued (in dollars per share)	13.05	$ 9.10
Vested (in dollars per share)	9.10
Forfeited (in dollars per share)	10.50
Balance, ending (in dollars per share)	$ 13.18
Restricted stock disclosures
Vesting period	3 years	3 years
Stock-based compensation	$ 741	$ 683
Unrecognized stock-based compensation expense	$ 8,500
Remaining weighted-average remaining vesting period	2 years 9 months 18 days