Earnings (loss) per share (EPS) - Schedule of Diluted Earnings Per Shares Calculation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Basic income (loss) per share
Net loss	$ (80)	$ (6,995)	$ 2,261	$ 6,885	$ (895)
Basic average shares outstanding (in shares)	49,115,000	48,830,000	49,083,000	48,696,000
Basic income (loss) per share (in dollars per share)	$ 0.00	$ (0.14)	$ 0.05	$ 0.14
Effect of stock options and awards outstanding:
Basic average shares outstanding (in shares)	49,115,000	48,830,000	49,083,000	48,696,000
Effect from dilutive shares and options outstanding (in shares)	0	0	767,000	719,000
Diluted weighted average shares (in shares)	49,115,000	48,830,000	49,850,000	49,415,000
Diluted income (loss) per share (in dollars per share)	$ 0.00	$ (0.14)	$ 0.05	$ 0.14