Commitments and Contingencies - Additional information (Details) - USD ($) $ in Millions	1 Months Ended	9 Months Ended	12 Months Ended
Oct. 31, 2020	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Commitments & Contingencies
Rent expense			$ 25.7	$ 24.8	$ 28.0
Sublease income			6.1	$ 2.7	$ 1.9
Maximum amount of new guarantee under lease agreement	$ 5.4	$ 3.1	$ 4.2

Amount of sublease income excluding finance and operating lease expense.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=123408670&loc=SL77918686-209980

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 55
-Paragraph 53
-URI http://asc.fasb.org/extlink&oid=123414884&loc=SL77918982-209971

Name:	us-gaap_SubleaseIncome
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration