Income Taxes - Effective Tax Rate Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended	12 Months Ended			13 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Jun. 30, 2017
Difference between the effective income tax provision rate and the U.S. federal statutory income tax provision rate
U.S. federal statutory income tax rate (as a percent)					21.00%	35.00%	35.00%
U.S. state income taxes, net of federal income tax benefit (as a percent)					(1.00%)	1.90%	1.90%
Foreign tax rate differences (as a percent)					6.80%	(3.40%)	(2.70%)
Tax on foreign dividends (as a percent)					3.60%		4.50%
Tax on foreign dividends						(0.30%)
Foreign financing structure (as a percent)					(5.10%)	(2.20%)	(1.60%)
Change in statutory rates (as a percent)					(3.90%)	(10.60%)	0.00%
Research and development and other tax credits (as a percent)					10.50%	3.30%	2.80%
Excess tax benefits from stock compensation (as a percent)					(2.90%)	(4.90%)	(3.00%)
Uncertain income tax positions (as a percent)					2.00%	0.80%	(0.40%)
Domestic production activities deduction (as a percent)					0.00%	0.60%	1.50%
Other differences - net (as a percent)					(0.50%)	0.00%	(0.70%)
Effective income tax rate (as a percent)					9.50%	12.40%	28.70%
Difference between the effective income tax provision and the U.S. federal statutory income tax provision
U.S. federal statutory income tax rate					$ 8.6	$ 32.1	$ 36.1
U.S. state income taxes, net of federal income tax benefit					(0.4)	1.7	2.0
Foreign tax rate differences					2.8	(3.1)	(2.8)
Tax on foreign dividends					1.5	(0.3)
Tax on foreign dividends							4.6
Foreign financing structure					(2.1)	(2.0)	(1.7)
Change in statutory tax rate, amount					(1.6)	(9.7)	0.0
Research and development and other credits					4.3	3.0	2.9
Excess tax benefits from stock compensation					(1.2)	(4.5)	(3.1)
Uncertain tax positions					0.8	0.7	(0.4)
Domestic production activities deduction					0.0	0.5	1.5
Other differences - net					(0.2)	0.0	(0.7)
Total provision for income taxes					3.9	11.4	29.6
Transition tax for accumulated foreign earnings, income tax expense (benefit)						3.8		$ 4.6
Measurement period adjustment to transition tax					0.8
Federal GILTI and state taxation of foreign earnings and profits					0.7
Change in tax rate effect on deferred taxes						10.3		$ 11.2
Measurement period tax benefit adjustment					0.9
Impairment loss	$ (2.9)	$ 2.0		$ 32.0	31.1	0.0	$ 0.0
Federal Ministry of Finance, Germany
Difference between the effective income tax provision and the U.S. federal statutory income tax provision
Change in statutory tax rate, amount						$ 0.6
Interest limitation									$ 4.1
Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations | Brattleboro Mill and Associated Research and Office Facilities
Difference between the effective income tax provision and the U.S. federal statutory income tax provision
Impairment loss			$ 32.0		31.1
Netherlands
Difference between the effective income tax provision and the U.S. federal statutory income tax provision
Change in statutory tax rate, amount	$ (0.7)				$ (0.7)