Acquisitions and Dispositions - Acquired Entities (Details) $ in Millions			3 Months Ended
	Jan. 04, 2019 USD ($) employee vehicle branch	Aug. 13, 2018 USD ($) employee vehicle branch	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill			$ 751.7	$ 678.6
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
Indemnification asset	(1.9)
Fair value of purchase consideration	131.2
Cash	1.4
Accounts receivable	8.2
Other current assets	0.4
Property and equipment, net	3.7
Intangible assets	47.9
Goodwill	80.4
Other noncurrent assets	5.1
Current liabilities	(9.6)
Noncurrent liabilities	(6.3)
Fair value of net assets acquired	131.2
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		57.0
Intangible assets		162.0
Goodwill		307.1
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