Income Taxes - Deferred Tax Asset/Liability (Details) - USD ($) $ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Deferred income tax assets (liabilities)
Net deferred income tax assets	$ 16.4		$ 10.1
Deferred income tax assets (liabilities)
Net deferred income tax liabilities	(14.4)		(15.0)
Retained earnings	243.2		235.7
Undistributed earnings of foreign subsidiaries	58.4		37.3
NOLs
Deferred tax asset related to net operating losses	3.0
Pre-acquisition built-in loss carryforward	8.5
Pre-acquisition built-in carryovers, deferred tax asset	1.8
Alternative minimum tax credit carryovers	1.4
Domestic Tax Authority
Deferred income tax assets (liabilities)
Research and development tax credits	20.0
Employee benefits	16.5
Net operating losses and other tax credits	7.4
Accrued liabilities	2.3
Interest limitation	1.7
Inventories	1.0
Other	0.5
Net deferred income tax assets	16.4
Deferred income tax assets (liabilities)
Accelerated depreciation	(28.8)
Intangibles	(4.2)
Wisconsin
Deferred income tax assets (liabilities)
Research and development tax credits			6.6
Employee benefits			1.1
Net operating losses and other tax credits			4.2
Accrued liabilities			0.1
Interest limitation			0.0
Inventories			0.2
Other			0.0
Net deferred income tax assets			10.1
Deferred income tax assets (liabilities)
Accelerated depreciation			(1.6)
Intangibles			(0.5)
State and Local Jurisdiction
NOLs
Net operating losses	47.6
Operating loss carryfowards, valuation allowance	0.5		0.4
Foreign Tax Authority
Deferred income tax assets (liabilities)
Research and development tax credits	0.0
Employee benefits	6.3
Accrued liabilities	0.0
Deferred income tax assets (liabilities)
Accelerated depreciation	(16.6)
Intangibles	(3.2)
Inventories	(1.0)
Net operating losses	0.2
Other	(0.1)
Net deferred income tax liabilities	(14.4)
Tax Authorities Other Than Wisconsin
Deferred income tax assets (liabilities)
Research and development tax credits			8.6
Employee benefits			22.9
Accrued liabilities			1.9
Inventories			1.8
Other			1.3
Deferred income tax assets (liabilities)
Accelerated depreciation			(45.1)
Intangibles			(11.4)
Net operating losses			5.0
Net deferred income tax liabilities			$ (15.0)
Research Tax Credit Carryforward | Domestic Tax Authority
NOLs
R & D credits subject to expiration	20.4
Research Tax Credit Carryforward | State and Local Jurisdiction
NOLs
R & D credits subject to expiration	$ 7.2
Accounting Standards Update 2016-06 | Domestic Tax Authority
Deferred income tax assets (liabilities)
Deferred income tax assets		$ 2.9
Retained earnings		2.9
Accounting Standards Update 2016-06 | Federal Ministry of Finance, Germany
Deferred income tax assets (liabilities)
Prepaid Taxes		3.7
Retained earnings		$ (3.7)