Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2018

Quarterly Financial Information Disclosure [Abstract]

Summary of Condensed Quarterly Results of Operations

The condensed quarterly results of operations for the years ended December 31, 2018 and 2017 (in thousands of dollars, except per share data) were as follows:

	Quarter Ended
	March 31,			June 30,			September 30,			December 31,
	2018			2018			2018			2018
	(Thousands of dollars, except per share data)
Operating revenues, net	$	160,370		$	169,243		$	168,787		$	176,023
(Loss) gain on disposition of assets, net	879			(171		)	—			45
(Loss) earnings before income taxes	(21,473		)	(8,777		)	(14,062		)	(123,148		)
Net (loss) earnings	(16,983		)	(7,093		)	(11,531		)	(105,907		)
Net (loss) earnings per share
Basic	(1.07		)	(0.45		)	(0.73		)	(6.70		)
Diluted	(1.07		)	(0.45		)	(0.73		)	(6.70		)
	Quarter Ended
	March 31,			June 30,			September 30,			December 31,
	2017			2017			2017			2017
	(Thousands of dollars, except per share data)
Operating revenues, net	$	134,618		$	146,424		$	150,167		$	148,336
Gain (loss) on disposition of assets, net	—			7			4			287
Earnings before income taxes	(23,073		)	(3,150		)	(4,899		)	(20,319		)
Net earnings	(15,248		)	(3,273		)	(3,277		)	29,330
Net earnings per share
Basic	(0.97		)	(0.21		)	(0.21		)	1.87
Diluted	(0.97		)	(0.21		)	(0.21		)	1.87