Reconciliation of Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator for basic (loss) earnings per share:
Net (loss) earnings	$ (45,445)	$ 2,317	$ (138,970)	$ 13,384
Numerator for diluted (loss) earnings per share:
Net (loss) earnings	(45,445)	2,317	(138,970)	13,384
Interest expense attributable to convertible notes				1,158
Net (loss) earnings plus interest expense attributable to convertible notes	$ (45,445)	$ 2,317	$ (138,970)	$ 14,542
Denominator for basic (loss) earnings per share:
Basic weighted average common shares outstanding during the period	21,071	20,916	20,996	18,928
Denominator for diluted (loss) earnings per share:
Basic weighted average common shares outstanding during the period	21,071	20,916	20,996	18,928
Net effect of dilutive convertible notes				1,163
Net effect of dilutive stock options and DSU's		279		290
Diluted weighted average common shares	21,071	21,195	20,996	20,381
Basic (in dollars per share)	$ (2.16)	$ 0.11	$ (6.62)	$ 0.71
Diluted (in dollars per share)	$ (2.16)	$ 0.11	$ (6.62)	$ 0.71
Antidilutive stock options excluded from weighted average share calculations (in shares)			1,200	1,200
Convertible Debt Notes
Denominator for diluted (loss) earnings per share:
Antidilutive stock options excluded from weighted average share calculations (in shares)			1,200