Accrued Liabilities (Tables)

12 Months Ended

Dec. 31, 2012

Accrued and Other Current Liabilities [Abstract]

Schedule of accrued liabilities

	2012		2011
	(Thousands of dollars)
Deferred revenue	$	76,410	$	—
Salaries & wages		15,920		8,699
Incentive compensation		6,253		3,029
Interest		5,649		5,877
Vacation payable		4,871		4,305
Group medical		1,845		1,695
Transportations tax		1,545		1,448
Operating lease		862		880
Workers compensation		1,137		678
Other		2,670		2,440
Total accrued liabilities	$	117,162	$	29,051