Acquisitions and Dispositions - Acquired Entities (Details) $ in Millions						3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2019 USD ($) employee	Jun. 14, 2019	Jun. 12, 2019	Jan. 04, 2019 USD ($) employee vehicle branch	Aug. 13, 2018 USD ($) employee vehicle branch	Sep. 30, 2019 USD ($) employee	Sep. 30, 2019 USD ($) employee acquisition	Dec. 31, 2018 USD ($)
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill	$ 776.0					$ 776.0	$ 776.0	$ 678.6
Other Acquisitions
Business Acquisition [Line Items]
Entity number of employees | employee	1,300					1,300	1,300
Number of Businesses Acquired | acquisition							3
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Purchase consideration - cash paid							$ 53.4
Fair value of future payments to sellers	$ 7.8					$ 7.8	7.8
Contingent consideration	1.6					1.6	1.6
Indemnification asset	(6.5)					(6.5)	(6.5)
Fair value of purchase consideration							56.3
Cash	5.1					5.1	5.1
Accounts receivable	4.5					4.5	4.5
Property and equipment, net	7.3					7.3	7.3
Intangible assets	21.6					21.6	21.6
Goodwill	36.5					36.5	36.5
Other noncurrent assets	2.4					2.4	2.4
Current liabilities	(14.8)					(14.8)	(14.8)
Noncurrent liabilities	(6.3)					(6.3)	(6.3)
Fair value of net assets acquired	$ 56.3					$ 56.3	$ 56.3
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%
TVS
Business Acquisition [Line Items]
Acquisition date	Sep. 30, 2019
Percentage of shares acquired	100.00%					100.00%	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				$ 135.7
Indemnification asset				(1.9)
Fair value of purchase consideration				133.8
Cash				1.4
Accounts receivable				9.2
Other current assets				0.5
Property and equipment, net				2.7
Intangible assets				47.9
Goodwill				84.3
Other noncurrent assets				5.3
Current liabilities				(9.6)
Noncurrent liabilities				(7.9)
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								21.0
Noncurrent assets increase								11.0
Noncurrent liability increase								16.0
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Purchase consideration - cash paid					$ 546.8
Receivable from seller						$ (6.3)		$ 6.0
Fair value of purchase consideration					540.5
Cash					25.8
Accounts receivable					31.9
Other current assets					11.7
Property and equipment, net					56.6
Intangible assets					162.0
Goodwill					304.1
Other noncurrent assets					21.1
Current liabilities					(29.5)
Noncurrent liabilities					(43.2)
Fair value of net assets acquired					540.5
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