Fair Value Measurements (Narrative) (Details) - USD ($) $ in Millions		3 Months Ended
	May 07, 2018	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accrued earnouts		$ 2.5	$ 2.5
Performance targets, maximum potential obligation		15.5	11.1
Treasury securities		0.2	0.2
Held-to-maturity investments, carrying value		0.5	0.5
Held-to-maturity investments, fair value		0.5	0.5
Business Combinations and Asset Acquisitions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Performance targets, maximum potential obligation		$ 3.1	$ 3.1
Revolving Credit Facility [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Basis spread on variable interest rate		1.375%
Revolving Credit Facility [Member] | Minimum [Member] | Subsequent Event [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Basis spread on variable interest rate	1.125%
Revolving Credit Facility [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Basis spread on variable interest rate		2.00%
Revolving Credit Facility [Member] | Maximum [Member] | Subsequent Event [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Basis spread on variable interest rate	1.75%