Income Taxes - Deferred Income Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Properties and equipment	$ 0.7	$ 1.9
Accrued expenses	28.6	27.3
Stock based compensation	3.9	3.5
Net operating loss and tax credit carryforwards	21.6	25.8
Goodwill and intangibles	1.5	0.9
Pension benefits	18.5	20.2
Gross deferred tax assets	74.8	79.6
Valuation allowance	(8.2)	(9.4)
Total deferred tax assets	66.6	70.2
Deferred tax liabilities:
Properties and equipment	(24.4)	(17.9)
Pension benefits	(11.3)	(10.3)
Goodwill and intangibles	(72.4)	(74.6)
Other	(1.1)	(1.1)
Gross deferred tax liabilities	(109.2)	(103.9)
Net deferred tax liabilities	$ (42.6)	$ (33.7)