Acquisitions - Additional Information (Details) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($) Center Business Business_Acquisition	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) Center Business	Dec. 31, 2018 USD ($)
Business Acquisition [Line Items]
Payments to acquire business, net of cash acquired	$ 8,101	$ 30,841
Consideration payable	0	16,621
Goodwill	1,409,040		$ 1,412,873	$ 1,347,611
Payment for contingent consideration	$ 1,088	$ 4,200
Trade names
Business Acquisition [Line Items]
Finite-lived intangible assets amortization period	6 years		6 years
Customer relationships
Business Acquisition [Line Items]
Finite-lived intangible assets amortization period	14 years		14 years
Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Number of businesses acquired | Business	3		8
Payments to acquire business, net of cash acquired	$ 8,100		$ 53,300
Cash acquired from acquisition	1,300		1,200
Consideration payable	100		700
Fixed assets and technology acquired	4,100
Payment for contingent consideration	$ 1,100		4,200
Contingent consideration (up to)			$ 20,000
Contingent consideration, term			3 years
Preliminary fair value estimate of contingent consideration			$ 13,900
Intangible assets			14,600
Fixed assets and technology acquired			3,100
Deferred tax liability			1,900
Number of business acquisitions open | Business_Acquisition	2
Series of Individually Immaterial Business Acquisitions | Series Of Individually Immaterial Business Acquisitions Completed In 2018
Business Acquisition [Line Items]
Payment for contingent consideration			3,500
Series of Individually Immaterial Business Acquisitions | Series Of Individually Immaterial Business Acquisitions Completed In 2016
Business Acquisition [Line Items]
Payment for contingent consideration			$ 700
Series of Individually Immaterial Business Acquisitions | Trade names
Business Acquisition [Line Items]
Finite-lived intangible assets acquired	$ 700
Finite-lived intangible assets amortization period	5 years
Series of Individually Immaterial Business Acquisitions | Customer relationships
Business Acquisition [Line Items]
Finite-lived intangible assets amortization period			5 years
Series of Individually Immaterial Business Acquisitions | Educational advisory and other services
Business Acquisition [Line Items]
Goodwill	$ 2,100		$ 14,000
Series of Individually Immaterial Business Acquisitions | Full service center-based child care
Business Acquisition [Line Items]
Goodwill	$ 2,100		15,200
Amount of goodwill expected to be deductible for tax purposes			3,900
Series of Individually Immaterial Business Acquisitions | Back-Up Care Services
Business Acquisition [Line Items]
Goodwill			$ 25,400
Series of Individually Immaterial Business Acquisitions | United States
Business Acquisition [Line Items]
Number of centers acquired | Center	2		3
Series of Individually Immaterial Business Acquisitions | Netherlands
Business Acquisition [Line Items]
Number of centers acquired | Center			4
Series of Individually Immaterial Business Acquisitions | United Kingdom
Business Acquisition [Line Items]
Number of centers acquired | Center			1