Summary of Significant Accounting Policies (Narrative) (Details) $ in Millions	3 Months Ended									12 Months Ended
	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) shares	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) customer segment shares	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jan. 01, 2018 USD ($)
Line of Credit Facility [Line Items]
Number of reportable segments | segment										3
Allowance for doubtful accounts		$ 4.5				$ 4.0				$ 4.5	$ 4.0
Sale of accounts receivable										80.0	81.6
Income (expense) related to discount on sale of accounts receivable										(0.6)	(0.5)
Unbilled contracts receivable		40.1				35.6				40.1	35.6
Billings in excess of revenues earned		23.0				22.7				$ 23.0	22.7
Number of customers with uncollateralized accounts receivable in automotive industry | customer										6
Uncollateralized accounts receivable		$ 42.7								$ 42.7
Percentage of accounts receivable uncollateralized										18.00%
Revenue from sales to major customers										$ 291.3
Percentage of revenue from sales to major customers		21.00%								21.00%
Share-based compensation, tax expense, ASU 2016-09										$ 0.2
Net sales		$ 366.0	$ 352.2	$ 350.9	$ 343.8	306.8	$ 312.7	$ 329.4	$ 328.0	1,412.9	1,276.9	$ 1,463.8
Retained earnings		$ 216.1				$ 193.6				$ 216.1	$ 193.6
2015 Long-Term Incentive Plan
Line of Credit Facility [Line Items]
Number of shares that may be awarded (in shares) | shares		98,586								98,586
2015 Long-Term Incentive Plan | Stock Options
Line of Credit Facility [Line Items]
Options maximum expiration period (more than)										10 years
Building | Minimum
Line of Credit Facility [Line Items]
Property, plant and equipment, useful life										5 years
Building | Maximum
Line of Credit Facility [Line Items]
Property, plant and equipment, useful life										40 years
Machinery and Equipment
Line of Credit Facility [Line Items]
Property, plant and equipment, useful life, majority range, minimum										3 years
Property, plant and equipment, useful life, majority range, maximum										10 years
Machinery and Equipment | Minimum
Line of Credit Facility [Line Items]
Property, plant and equipment, useful life										1 year
Machinery and Equipment | Maximum
Line of Credit Facility [Line Items]
Property, plant and equipment, useful life										20 years
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09 | Scenario, Forecast | Minimum
Line of Credit Facility [Line Items]
Net sales	$ 13.0
Retained earnings													$ 2.0
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09 | Scenario, Forecast | Maximum
Line of Credit Facility [Line Items]
Net sales	$ 17.0
Retained earnings													$ 4.0