NET INCOME (LOSS) PER COMMON SHARE (Tables)

12 Months Ended

Dec. 31, 2018

Earnings Per Share [Abstract]

Net Income (Loss) Per Common Share

	Year ended December 31,
	2018			2017		2016
	(thousands of dollars)
Net income (loss)	$	(2,332	)	$	18,009	$	19,428
Basic earnings (loss) per common share:
Weighted average shares outstanding	24,438			24,294		24,284
Per share amount (dollars)	$	(0.10	)	$	0.74	$	0.80
Diluted earnings (loss) per common share:
Weighted average shares outstanding	24,438			25,129		24,982
Per share amount (dollars)	$	(0.10	)	$	0.72	$	0.78
Weighted average shares-denominator   basic computation	24,438			24,294		24,284
Unvested restricted stock unit grant	—			367		310
Effect of dilutive stock options	—			468		388
Weighted average shares, as adjusted   denominator diluted computation	24,438			25,129		24,982