Business Acquisitions Business Acquisition - Recognized Intangible Assets, Goodwill and Earn-Out Provisions (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019	Aug. 23, 2019	Jan. 01, 2019	Dec. 31, 2018	Dec. 01, 2018	Oct. 01, 2018	Aug. 01, 2018	Jul. 01, 2018	Apr. 01, 2018	Feb. 01, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill	$ 952,404				$ 946,685							$ 666,863
Derivative liability	10,095				24,976							$ 37,096
Indus
Business Acquisition [Line Items]
Derivative liability	0
Miles
Business Acquisition [Line Items]
Derivative liability	7,700
Essel
Business Acquisition [Line Items]
Derivative liability	396
Zillious
Business Acquisition [Line Items]
Derivative liability		$ 1,500
Final Allocation
Business Acquisition [Line Items]
Goodwill	17,932				322,624
Intangible assets, gross (excluding goodwill)	3,038				20,437
Derivative liability	$ 1,922				$ 8,581
Final Allocation | Transcorp
Business Acquisition [Line Items]
Goodwill											$ 7,254
Intangible assets, gross (excluding goodwill)											0
Derivative liability											$ 0
Final Allocation | CDL (Centrum)
Business Acquisition [Line Items]
Goodwill										$ 159,647
Intangible assets, gross (excluding goodwill)										5,742
Derivative liability										0
Final Allocation | Smartclass
Business Acquisition [Line Items]
Goodwill										16,568
Intangible assets, gross (excluding goodwill)										4,243
Derivative liability										$ 0
Final Allocation | Indus
Business Acquisition [Line Items]
Goodwill									$ 21,501
Intangible assets, gross (excluding goodwill)									2,146
Derivative liability									3,310
Final Allocation | Leisure
Business Acquisition [Line Items]
Goodwill									1,699
Intangible assets, gross (excluding goodwill)									202
Derivative liability									0
Final Allocation | Mercury
Business Acquisition [Line Items]
Goodwill									15,127
Intangible assets, gross (excluding goodwill)									1,051
Derivative liability									$ 0
Final Allocation | Miles
Business Acquisition [Line Items]
Goodwill								$ 19,075
Intangible assets, gross (excluding goodwill)								5,048
Derivative liability								$ 5,271
Final Allocation | AHA Taxis
Business Acquisition [Line Items]
Goodwill							$ 592
Intangible assets, gross (excluding goodwill)							0
Derivative liability							0
Final Allocation | Business Travels,Global Business Travels , and Subizz Travel
Business Acquisition [Line Items]
Goodwill							1,102
Intangible assets, gross (excluding goodwill)							0
Derivative liability							0
Final Allocation | Routier
Business Acquisition [Line Items]
Goodwill							698
Intangible assets, gross (excluding goodwill)							0
Derivative liability							$ 0
Final Allocation | Lawson
Business Acquisition [Line Items]
Goodwill						$ 4,437
Intangible assets, gross (excluding goodwill)						0
Derivative liability						0
Final Allocation | Pearl
Business Acquisition [Line Items]
Goodwill						3,372
Intangible assets, gross (excluding goodwill)						0
Derivative liability						0
Final Allocation | Weizmann
Business Acquisition [Line Items]
Goodwill						71,552
Intangible assets, gross (excluding goodwill)						2,005
Derivative liability						$ 0
Final Allocation | Essel
Business Acquisition [Line Items]
Goodwill				$ 8,372
Intangible assets, gross (excluding goodwill)				1,163
Derivative liability				407
Final Allocation | Zillious
Business Acquisition [Line Items]
Goodwill				9,489
Intangible assets, gross (excluding goodwill)				1,875
Derivative liability				$ 1,515
Final Allocation | Wallstreet Canada
Business Acquisition [Line Items]
Goodwill			$ 71
Intangible assets, gross (excluding goodwill)			0
Derivative liability			$ 0