Income Taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2012 Rate	Dec. 31, 2011 Rate	Dec. 31, 2010 Rate
Income before income taxes
Income before income taxes	$ 40,658,000	$ 23,300,000	$ 24,334,000
Provision for income taxes
Federal	15,853,000	3,065,000	4,051,000
State	2,239,000	2,277,000	1,057,000
Canadian	1,578,000	1,565,000	1,789,000
Total current	19,670,000	6,907,000	6,897,000
Deferred taxes	(3,607,000)	2,328,000	3,384,000
Total taxes on income	16,063,000	9,235,000	10,281,000
Tax rate reconciliation
Statutory U.S. federal tax rate	35.00%	35.00%	35.00%
State income taxes, net of federal benefit	3.90%	5.10%	3.20%
Effect of Canadian income taxes	(1.00%)	(1.20%)	(1.00%)
Nondeductible expenses	1.40%	2.50%	2.00%
ESOP dividend deduction	(0.70%)	(1.20%)	(1.10%)
U.S. tax benefit of foreign source income	0.00%	(0.10%)	(0.70%)
Valuation allowance on foreign tax credits	0.00%	(1.10%)	4.20%
All other, net	0.90%	0.60%	0.60%
Effective income tax rate	39.50%	39.60%	42.20%
Current deferred tax assets and liabilities, net
Accrued compensation obligations	2,424,000	2,182,000
Self-insurance accruals	7,083,000	9,303,000
Other, net	(498,000)	893,000
Deferred tax assets, current, gross	9,009,000	12,378,000
Less deferred tax asset valuation allowance	194,000	307,000
Net deferred income tax assets--current	8,815,000	12,071,000
Noncurrent deferred tax assets and liabilities, net
Self-insurance accruals	14,497,000	10,491,000
Intangibles	(341,000)	424,000
Accrued expenses and other liabilities	895,000	700,000
Accrued stock compensation	1,476,000	1,395,000
Defined benefit pension plans	4,698,000	3,702,000
Foreign tax credit carryforward	768,000	768,000
Other future deductible amounts, net	1,470,000	1,392,000
Deferred tax assets, gross, noncurrent	23,463,000	18,872,000
Less deferred tax asset valuation allowance	574,000	461,000
Deferred tax assets, net of valuation allowance	22,889,000	18,411,000
Property and equipment	21,830,000	24,044,000
Deferred tax liability, noncurrent	21,830,000	24,044,000
Net deferred tax assets--noncurrent	1,059,000	0
Net deferred tax liabilities--noncurrent	0	5,633,000
Undistributed Earnings of Foreign Subsidiaries	24,800,000
Unrecognized benefits and related interest and penalties
Unrecognized tax benefits	2,638,000	1,825,000	1,524,000
Portion, if recognized, would reduce tax expense and effective tax rate	1,933,000	1,260,000
Accrued interest on unrecognized tax benefits	142,000	99,000
Accrued penalties on unrecognized benefits	0	0
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Estimated Range of Change, Lower Bound	500
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Estimated Range of Change, Upper Bound	800
Reconciliation of unrecognized tax benefits
Balance, beginning of year	1,825,000	1,524,000	2,165,000
Additions based on tax positions related to the current year	667,000	279,000	372,000
Additions for tax positions of prior years	149,000	101,000	1,185,000
Reductions for tax positions of prior years	(3,000)	(61,000)	(232,000)
Reductions related to settlements with taxing authorities	0	0	(900,000)
Lapses in statutes of limitations	0	(18,000)	(1,066,000)
Balance, end of year	2,638,000	1,825,000	1,524,000
United States [Member]
Income before income taxes
Income before income taxes	35,414,000	18,261,000	18,549,000
Canada [Member]
Income before income taxes
Income before income taxes	$ 5,244,000	$ 5,039,000	$ 5,785,000