Acquisitions and Dispositions - Acquired Entities (Details)									6 Months Ended	12 Months Ended
	May 31, 2018 USD ($)	Jan. 10, 2018 USD ($)	Oct. 31, 2017	Aug. 14, 2017	Jul. 18, 2017 USD ($) employee vehicle branch	Jun. 29, 2017	Apr. 19, 2017	Mar. 14, 2017	Jun. 30, 2018 USD ($) employee acquisition	Dec. 31, 2017 USD ($) acquisition
Business Acquisition [Line Items]
Number of acquired operations | acquisition										6
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill									$ 375,000,000	$ 453,700,000
Maco
Business Acquisition [Line Items]
Acquisition date					Jul. 18, 2017
Percentage of shares acquired					100.00%
Scheduled installments period					2 years
Potential undiscounted amount minimum					$ 0
Potential undiscounted amount maximum					$ 30,300,000.0				$ 30,300,000
Revenue multiple					2.5
Entity number of employees | employee					1,450
Entity Number of branches | branch					4
Entity Number of armored vehicles | vehicle					150
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Purchase consideration - cash paid					$ 173,900,000
Fair value of future payments to sellers					1,900,000
Contingent consideration					28,700,000
Fair value of purchase consideration					204,500,000
Cash					10,300,000
Accounts receivable					16,600,000
Other current assets					600,000
Property and equipment, net					2,400,000
Intangible assets					60,200,000
Goodwill					147,600,000
Other noncurrent assets					100,000
Current liabilities					(11,800,000)
Noncurrent liabilities					(21,500,000)
Fair value of net assets acquired					$ 204,500,000
Other Acquisitions
Business Acquisition [Line Items]
Number of acquired operations | acquisition									5
Entity number of employees | employee									1,700
Goodwill increase									$ 9,000,000
Intangible assets decrease									10,000,000
Noncurrent liability increase									11,000,000
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Purchase consideration - cash paid									160,400,000
Indemnification Assets									(9,600,000)
Fair value of future payments to sellers									3,900,000
Fair value of purchase consideration									154,700,000
Cash									7,400,000
Accounts receivable									20,100,000
Property and equipment, net									14,000,000
Intangible assets									40,600,000
Goodwill									114,200,000
Other noncurrent assets									7,300,000
Current liabilities									(23,500,000)
Noncurrent liabilities									(25,400,000)
Fair value of net assets acquired									$ 154,700,000
AATI
Business Acquisition [Line Items]
Acquisition date								Mar. 14, 2017
Percentage of shares acquired								100.00%
Pag Facil
Business Acquisition [Line Items]
Acquisition date							Apr. 19, 2017
Percentage of shares acquired							100.00%
LGS
Business Acquisition [Line Items]
Acquisition date						Jun. 29, 2017
Percentage of shares acquired						100.00%
Maco Litoral
Business Acquisition [Line Items]
Acquisition date				Aug. 14, 2017
Percentage of shares acquired				100.00%
Temis
Business Acquisition [Line Items]
Acquisition date			Oct. 31, 2017
Percentage of shares acquired			100.00%
Rodoban
Business Acquisition [Line Items]
Date of Acquisition Announced		Jan. 10, 2018
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Purchase consideration - cash paid		$ 145,000,000
Dunbar
Business Acquisition [Line Items]
Date of Acquisition Announced	May 31, 2018
Annual revenues	$ 390,000,000	$ 80,000,000
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Purchase consideration - cash paid	$ 520,000,000