Acquisitions and Dispositions - Acquired Entities (Details) $ in Millions					6 Months Ended	12 Months Ended
	Jun. 14, 2019	Jun. 12, 2019	Jan. 04, 2019 USD ($) employee vehicle branch	Aug. 13, 2018 USD ($) employee vehicle branch	Jun. 30, 2019 USD ($) employee acquisition	Dec. 31, 2018 USD ($)
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill					$ 782.5	$ 678.6
Other Acquisitions
Business Acquisition [Line Items]
Entity number of employees | employee					400
Number of Businesses Acquired | acquisition					2
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Purchase consideration - cash paid					$ 39.0
Contingent consideration					1.6
Indemnification asset					(0.3)
Fair value of purchase consideration					40.3
Cash					5.3
Accounts receivable					1.9
Property and equipment, net					2.3
Intangible assets					15.9
Goodwill					23.3
Other noncurrent assets					1.0
Current liabilities					(7.6)
Noncurrent liabilities					(1.8)
Fair value of net assets acquired					$ 40.3
BI
Business Acquisition [Line Items]
Acquisition date		Jun. 12, 2019
Percentage of shares acquired		100.00%
COMEF
Business Acquisition [Line Items]
Acquisition date	Jun. 14, 2019
Percentage of shares acquired	100.00%
Rodoban
Business Acquisition [Line Items]
Acquisition date			Jan. 04, 2019
Percentage of shares acquired			100.00%
Annual revenues			$ 80.0
Entity number of employees | employee			2,900
Entity Number of branches | branch			13
Entity Number of armored vehicles | vehicle			190
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Purchase consideration - cash paid			$ 133.1
Fair value of future payments to sellers			2.6
Indemnification asset			(1.9)
Fair value of purchase consideration			133.8
Cash			1.4
Accounts receivable			8.2
Other current assets			0.5
Property and equipment, net			3.7
Intangible assets			47.9
Goodwill			84.1
Other noncurrent assets			5.3
Current liabilities			(9.6)
Noncurrent liabilities			(7.7)
Fair value of net assets acquired			133.8
Dunbar
Business Acquisition [Line Items]
Acquisition date				Aug. 13, 2018
Percentage of shares acquired				100.00%
Entity number of employees | employee				5,400
Entity Number of branches | branch				78
Entity Number of armored vehicles | vehicle				1,600
Intangible assets decrease						20.0
Goodwill increase						24.0
Noncurrent assets increase						11.0
Noncurrent liability increase						$ 13.0
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Purchase consideration - cash paid				$ 546.8
Fair value of purchase consideration				546.8
Cash				25.8
Accounts receivable				31.9
Other current assets				11.7
Property and equipment, net				57.4
Intangible assets				162.0
Goodwill				306.7
Other noncurrent assets				21.1
Current liabilities				(29.7)
Noncurrent liabilities				(40.1)
Fair value of net assets acquired				546.8
Customer relationships | Rodoban
Business Acquisition [Line Items]
Remaining Amortization Period					11 years
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Intangible assets			46.0
Customer relationships | Dunbar
Business Acquisition [Line Items]
Remaining Amortization Period					15 years
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Intangible assets				148.0
Trade names | Rodoban
Business Acquisition [Line Items]
Remaining Amortization Period					1 year
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Intangible assets			1.0
Trade names | Dunbar
Business Acquisition [Line Items]
Remaining Amortization Period					8 years
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Intangible assets				$ 14.0
Noncompete agreements | Rodoban
Business Acquisition [Line Items]
Remaining Amortization Period					5 years
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Intangible assets			$ 1.0