Income Taxes - Deferred Income Tax Assets and Liabilities (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Accrued liabilities		$ 17.1	$ 13.7
Employee benefits and compensation		37.7	21.1
Inventories		12.6	15.4
Net operating loss carryforwards		34.4	38.1
Restricted stock and performance units		10.2	9.0
Pension and postretirement benefits		87.4	90.6
Derivatives		4.7	6.1
Capital loss and general business credit carryforwards		3.3	3.2
Gross deferred tax assets		207.4	197.2
Valuation allowance	[1]	(3.1)	(3.1)
Net deferred tax assets		204.3	194.1
Deferred tax liabilities:
Property, plant and equipment		(422.3)	(368.6)
Goodwill and intangible assets		(67.2)	(65.0)
Total deferred tax liabilities		(489.5)	(433.6)
Net deferred tax liabilities	[2]	$ (285.2)	$ (239.5)

[1] Deferred tax assets are reduced by a valuation allowance when it is more likely than not that some portion of the deferred tax assets will not be realized. Both the 2018 and 2017 valuation allowance relates to capital losses. We do not expect to generate capital gains before the capital losses expire. If or when recognized, the tax benefits relating to the reversal of any or all of the valuation allowance would be recognized as a benefit to income tax expense.

[2] As of December 31, 2018, we did not recognize U.S. deferred income taxes on our cumulative total of undistributed foreign earnings for our foreign subsidiaries. We indefinitely reinvest our earnings in operations outside the United States. It is not practicable to determine the amount of unrecognized deferred tax liability on these undistributed earnings because the actual tax liability, if any, is dependent on circumstances existing when the repatriation occurs.