Acquisitions and Dispositions - Acquired Entities (Details)									3 Months Ended	9 Months Ended	12 Months Ended
	Aug. 13, 2018 USD ($) employee vehicle branch	Jan. 10, 2018 USD ($)	Oct. 31, 2017	Aug. 14, 2017	Jul. 18, 2017 USD ($) employee vehicle branch	Jun. 29, 2017	Apr. 19, 2017	Mar. 14, 2017	Sep. 30, 2018 USD ($) employee	Sep. 30, 2018 USD ($) employee acquisition	Dec. 31, 2017 USD ($) acquisition
Business Acquisition [Line Items]
Number of acquired operations | acquisition										1	6
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill									$ 651,900,000	$ 651,900,000	$ 453,700,000
Other Acquisitions
Business Acquisition [Line Items]
Number of acquired operations | acquisition										5
Entity number of employees | employee									1,700	1,700
Goodwill increase										$ 9,000,000
Intangible assets decrease										10,000,000
Noncurrent liability increase										12,000,000
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Purchase consideration - cash paid										160,400,000
Indemnification asset									$ (9,800,000)	(9,800,000)
Fair value of future payments to sellers									3,900,000	3,900,000
Fair value of purchase consideration										154,500,000
Cash									7,400,000	7,400,000
Accounts receivable									20,000,000	20,000,000
Property and equipment, net									14,000,000	14,000,000
Intangible assets									40,600,000	40,600,000
Goodwill									114,200,000	114,200,000
Other noncurrent assets									7,300,000	7,300,000
Current liabilities									(23,400,000)	(23,400,000)
Noncurrent liabilities									(25,600,000)	(25,600,000)
Fair value of net assets acquired									$ 154,500,000	154,500,000
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%
Maco
Business Acquisition [Line Items]
Acquisition date					Jul. 18, 2017
Percentage of shares acquired					100.00%
Entity number of employees | employee					1,450
Entity Number of branches | branch					4
Entity Number of armored vehicles | vehicle					150
Scheduled installments period									1 year 3 months
Potential undiscounted amount minimum					$ 0
Potential undiscounted amount maximum					30,300,000.0				$ 30,300,000	$ 30,300,000
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Purchase consideration - cash paid					174,200,000
Indemnification asset					(300,000)
Fair value of future payments to sellers					1,800,000
Contingent consideration					28,700,000
Fair value of purchase consideration					204,400,000
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					147,300,000
Other noncurrent assets					100,000
Current liabilities					(11,800,000)
Noncurrent liabilities					(21,300,000)
Fair value of net assets acquired					$ 204,400,000
Rodoban
Business Acquisition [Line Items]
Date of Acquisition Announced		Jan. 10, 2018
Annual revenues		$ 80,000,000
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Purchase consideration - cash paid		$ 145,000,000
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
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Purchase consideration - cash paid	$ 546,800,000
Fair value of purchase consideration	546,800,000
Cash	25,800,000
Accounts receivable	31,900,000
Other current assets	11,300,000
Property and equipment, net	56,800,000
Intangible assets	182,000,000
Goodwill	282,700,000
Other noncurrent assets	9,700,000
Current liabilities	(26,100,000)
Noncurrent liabilities	(27,300,000)
Fair value of net assets acquired	$ 546,800,000
Measurement Input, Revenue Multiple | Maco
Business Acquisition [Line Items]
Revenue multiple					2.5