Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Employee benefits, including post-retirement benefits	$ 11,900,000	$ 11,800,000
Trade and other receivables	4,100,000	3,700,000
Inventories	4,100,000	0
Self-insurance reserves	2,400,000	2,600,000
ROU liabilities	80,100,000	70,000,000.0
Other	3,100,000	3,000,000.0
Subtotal	105,700,000	91,100,000
Less: validation allowance	(600,000)	(1,700,000)	$ 0
Total deferred tax assets	105,100,000	89,400,000
Deferred tax liabilities:
Inventories	0	13,100,000
Property and equipment	26,900,000	29,100,000
ROU assets	75,100,000	65,300,000
Goodwill and intangibles	3,000,000.0	2,800,000
Other	2,200,000	1,700,000
Total deferred tax liabilities	107,200,000	112,000,000.0
Net deferred tax liabilities	(2,100,000)	(22,600,000)
Net deferred liability	(2,100,000)	(22,600,000)
Canada
Deferred tax liabilities:
Net deferred liability	(600,000)	(500,000)
U.S.
Deferred tax liabilities:
Net deferred liability	$ (1,500,000)	$ (22,100,000)