Condensed Consolidated Statements of Mezzanine Equity and Stockholders' Deficiency (Unaudited) - USD ($) $ in Thousands		Total	Reclassification of Redeemable Common Shares from Temporary to Permanent Equity [Member]	Reclassification of Share-based Awards from Liabilities and Temporary Equity to Permanent Equity [Member]	Redeemable Convertible Preferred Stock [Member]	Temporary Equity [Member] Redeemable Convertible Preferred Stock [Member]	Temporary Equity [Member] Redeemable Convertible Preferred Stock [Member] Reclassification of Redeemable Common Shares from Temporary to Permanent Equity [Member]	Temporary Equity [Member] Redeemable Convertible Preferred Stock [Member] Reclassification of Share-based Awards from Liabilities and Temporary Equity to Permanent Equity [Member]	Temporary Equity [Member] Redeemable Common Shares [Member]	Temporary Equity [Member] Redeemable Common Shares [Member] Reclassification of Redeemable Common Shares from Temporary to Permanent Equity [Member]	Temporary Equity [Member] Redeemable Common Shares [Member] Reclassification of Share-based Awards from Liabilities and Temporary Equity to Permanent Equity [Member]	Temporary Equity [Member] Share-based Awards [Member]	Temporary Equity [Member] Share-based Awards [Member] Reclassification of Redeemable Common Shares from Temporary to Permanent Equity [Member]	Temporary Equity [Member] Share-based Awards [Member] Reclassification of Share-based Awards from Liabilities and Temporary Equity to Permanent Equity [Member]	Noncontrolling Interest [Member]	Noncontrolling Interest [Member] Reclassification of Redeemable Common Shares from Temporary to Permanent Equity [Member]	Noncontrolling Interest [Member] Reclassification of Share-based Awards from Liabilities and Temporary Equity to Permanent Equity [Member]	Temporary Equity, Including Portion Attributable to Noncontrolling Interests [Member]	Temporary Equity, Including Portion Attributable to Noncontrolling Interests [Member] Reclassification of Redeemable Common Shares from Temporary to Permanent Equity [Member]	Temporary Equity, Including Portion Attributable to Noncontrolling Interests [Member] Reclassification of Share-based Awards from Liabilities and Temporary Equity to Permanent Equity [Member]	Common Stock [Member]		Common Stock [Member] Reclassification of Redeemable Common Shares from Temporary to Permanent Equity [Member]	[1]	Common Stock [Member] Reclassification of Share-based Awards from Liabilities and Temporary Equity to Permanent Equity [Member]	[1]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Reclassification of Redeemable Common Shares from Temporary to Permanent Equity [Member]	Additional Paid-in Capital [Member] Reclassification of Share-based Awards from Liabilities and Temporary Equity to Permanent Equity [Member]	Treasury Stock [Member]	Treasury Stock [Member] Reclassification of Redeemable Common Shares from Temporary to Permanent Equity [Member]	Treasury Stock [Member] Reclassification of Share-based Awards from Liabilities and Temporary Equity to Permanent Equity [Member]	Retained Earnings [Member]	Retained Earnings [Member] Reclassification of Redeemable Common Shares from Temporary to Permanent Equity [Member]	Retained Earnings [Member] Reclassification of Share-based Awards from Liabilities and Temporary Equity to Permanent Equity [Member]	AOCI Attributable to Parent [Member]	AOCI Attributable to Parent [Member] Reclassification of Redeemable Common Shares from Temporary to Permanent Equity [Member]	AOCI Attributable to Parent [Member] Reclassification of Share-based Awards from Liabilities and Temporary Equity to Permanent Equity [Member]
Balance, temporary equity, shares (in shares) at Dec. 31, 2019						51,091,344
Balance, temporary equity, including noncontrolling interest at Dec. 31, 2019						$ 182,656			$ 10,684			$ 1,291			$ 0			$ 194,631
Balance (in shares) at Dec. 31, 2019	[1]																				84,331,573
Balance at Dec. 31, 2019		$ (198,682)																			$ 10	[1]					$ 33,691			$ 0			$ (233,957)			$ 1,574
Reclassification of common shares to mezzanine equity		(97)				0			0			97			0			97			0	[1]					(97)			0			0			0
Remeasurement of redemption value of common shares		(6,244)				0			6,244			0			0			6,244			$ 0	[1]					0			0			(6,244)			0
Proceeds from exercise of options (in shares)	[1]																				121,680
Proceeds from exercise of options		54																			$ 0	[1]					54			0			0			0
Stock-based compensation expense		1,803																			0	[1]					1,803			0			0			0
Remeasurement of redemption value of convertible preferred stock		(19,943)				19,943			0			0			0			19,943			0	[1]								0			(19,943)			0
Net loss		(4,870)																			0	[1]					0			0			(4,870)			0
Net loss attributable to and accretion of redeemable noncontrolling interest		0
Foreign currency translation adjustment						0			0			0			0			0
Foreign currency translation adjustment		(274)																			0	[1]					0			0			0			(274)
Reclassification of share-based awards to mezzanine equity		(97)				$ 0			0			97			0			97			$ 0	[1]					(97)			0			0			0
Proceeds from the issuance of common stock, net of issuance costs (in shares)	[1]																				11,770,461
Proceeds from the issuance of common stock, net of issuance costs		54,979																			$ 1	[1]					54,978			0			0			0
Issuance of common shares in exchange for issuance cost (in shares)	[1]																				391,115
Issuance of common shares in exchange for issuance cost		2,408																			$ 0	[1]					2,408			0			0			0
Redemption of Series B convertible preferred stock (in shares)						(9,090,752)
Redemption of Series B convertible preferred stock						$ (32,242)			0			0			0			(32,242)
Redemption of Series B convertible preferred stock		(1,470)																			$ 0	[1]					0			0			(1,470)			0
Net income						$ 0			0			0			0			0
Balance, temporary equity, shares (in shares) at Sep. 30, 2020						42,000,592
Balance, temporary equity, including noncontrolling interest at Sep. 30, 2020						$ 170,357			16,928			1,388			0			188,673
Balance (in shares) at Sep. 30, 2020	[1]																				96,614,829
Balance at Sep. 30, 2020		(172,336)																			$ 11	[1]					92,837			0			(266,484)			1,300
Balance, temporary equity, shares (in shares) at Jun. 30, 2020						51,091,344
Balance, temporary equity, including noncontrolling interest at Jun. 30, 2020						$ 198,454			10,699			1,287			0			210,440
Balance (in shares) at Jun. 30, 2020	[1]																				90,643,593
Balance at Jun. 30, 2020		(182,682)																			$ 11	[1]					58,429			0			(242,455)			1,333
Reclassification of common shares to mezzanine equity		(101)				0			0			101			0			101			0	[1]					(101)			0			0			0
Remeasurement of redemption value of common shares		(6,229)				0			6,229			0			0			6,229			$ 0	[1]					0			0			(6,229)			0
Proceeds from exercise of options (in shares)	[1]																				91,260
Proceeds from exercise of options		39																			$ 0	[1]					39			0			0			0
Stock-based compensation expense		853																			0	[1]					853			0			0			0
Remeasurement of redemption value of convertible preferred stock		(4,145)				4,145			0			0			0			4,145			0	[1]					0			0			(4,145)			0
Net loss		(12,185)																			0	[1]					0			0			(12,185)			0
Net loss attributable to and accretion of redeemable noncontrolling interest		0
Foreign currency translation adjustment						0			0			0			0			0
Foreign currency translation adjustment		(33)																			0	[1]					0			0			0			(33)
Reclassification of share-based awards to mezzanine equity		(101)				$ 0			0			101			0			101			$ 0	[1]					(101)			0			0			0
Proceeds from the issuance of common stock, net of issuance costs (in shares)	[1]																				5,488,862
Proceeds from the issuance of common stock, net of issuance costs		31,209																			$ 0	[1]					31,209			0			0			0
Issuance of common shares in exchange for issuance cost (in shares)	[1]																				391,115
Issuance of common shares in exchange for issuance cost		2,408																			$ 0	[1]					2,408			0			0			0
Redemption of Series B convertible preferred stock (in shares)						(9,090,752)
Redemption of Series B convertible preferred stock						$ (32,242)			0			0			0			(32,242)
Redemption of Series B convertible preferred stock		(1,470)																			$ 0	[1]					0			0			(1,470)			0
Net income						$ 0			0			0			0			0
Balance, temporary equity, shares (in shares) at Sep. 30, 2020						42,000,592
Balance, temporary equity, including noncontrolling interest at Sep. 30, 2020						$ 170,357			16,928			1,388			0			188,673
Balance (in shares) at Sep. 30, 2020	[1]																				96,614,829
Balance at Sep. 30, 2020		(172,336)																			$ 11	[1]					92,837			0			(266,484)			1,300
Balance, temporary equity, shares (in shares) at Dec. 31, 2020					42,001	42,000,592
Balance, temporary equity, including noncontrolling interest at Dec. 31, 2020		213,014				$ 183,390			25,074			1,489			3,061			213,014
Balance (in shares) at Dec. 31, 2020	[1]																				100,068,469
Balance at Dec. 31, 2020		(192,827)																			$ 12	[1]					105,159			0			(299,789)			1,791
Reclassification of common shares to mezzanine equity		(206)				0			0			206			0			206			0	[1]					(206)			0			0			0
Remeasurement of redemption value of common shares		$ (7,361)				0			7,361			0			0			7,361			$ 0	[1]					0			0			(7,361)			0
Proceeds from exercise of options (in shares)		4,503,176																			4,503,176	[1]
Proceeds from exercise of options		$ 7,232																			$ 0	[1]					7,232			0			0			0
Stock-based compensation expense		37,441																			0	[1]					37,441			0			0			0
Remeasurement of redemption value of convertible preferred stock		(32,928)				$ 32,928			0			0			0			32,928			$ 0	[1]					0			0			(32,928)			0
Conversion of convertible preferred stock (in shares)						(42,000,592)
Conversion of convertible preferred stock						$ (216,318)			0			0			0			(216,318)
Conversion of convertible preferred stock (in shares)	[1]																				28,500,592
Conversion of convertible preferred stock		85,393																			$ 3	[1]					85,390			0			0			0
Reclassification of temporary equity to permanent equity			$ 39,307	$ 41,152			$ 0	$ 0		$ (39,307)	$ 0		$ 0	$ (1,695)		$ 0	$ 0		$ (39,307)	$ (1,695)			$ 0		$ 0			$ 39,307	$ 41,152		$ 0	$ 0		$ 0	$ 0		$ 0	$ 0
Merger and recapitalization, net of transaction costs (in shares)	[1]																				47,940,523
Merger and recapitalization, net of transaction costs		299,163																			$ 3	[1]					299,160			0			0			0
Reclassification of earn-out RSUs to earn-out shares		(581)																			0	[1]					(581)			0			0			0
Reclassification of Apex shares purchased prior to the Business Combination		(1,739)																			0	[1]					0			(1,739)			0			0
Net loss		(25,756)																			0	[1]					0			0			(25,756)			0
Net loss attributable to and accretion of redeemable noncontrolling interest						0			0			0			1,413			1,413
Net loss attributable to and accretion of redeemable noncontrolling interest		(1,413)																			0	[1]					0			0			(1,413)			0
Foreign currency translation adjustment						0			0			0			(81)			(81)
Foreign currency translation adjustment		101																			0	[1]					0			0			0			101
Reclassification of share-based awards to mezzanine equity		(206)				0			0			206			0			206			0	[1]					(206)			0			0			0
Reclassification of common shares to mezzanine equity						0			6,872			0			0			6,872
Issuance of redeemable noncontrolling interest in EduTech						0			0			0			238			238
Issuance of redeemable noncontrolling interest in EduTech		515																			$ 0	[1]					515			0			0			0
Net loss attributable to and accretion of redeemable noncontrolling interest						$ 0			0			0			1,413			1,413
Balance, temporary equity, shares (in shares) at Sep. 30, 2021						0
Balance, temporary equity, including noncontrolling interest at Sep. 30, 2021		4,631				$ 0			0			0			4,631			4,631
Balance (in shares) at Sep. 30, 2021	[1]																				181,012,760
Balance at Sep. 30, 2021	[1]	247,493																			$ 18						614,569			(1,739)			(367,247)			1,892
Balance, temporary equity, shares (in shares) at Jun. 30, 2021						42,000,592
Balance, temporary equity, including noncontrolling interest at Jun. 30, 2021						$ 216,926			39,757			1,695			4,143			262,521
Balance (in shares) at Jun. 30, 2021	[1]																				103,831,523
Balance at Jun. 30, 2021		(243,217)																			$ 12	[1]					112,953			0			(358,030)			1,848
Reclassification of common shares to mezzanine equity						0			(1)			0			0			(1)
Remeasurement of redemption value of common shares		$ 449				0			(449)			0			0			(449)			$ 0	[1]					0			0			449			0
Proceeds from exercise of options (in shares)		740,122																			740,122	[1]
Proceeds from exercise of options		$ 3,955																			$ 0	[1]					3,955			0			0			0
Stock-based compensation expense		33,233																			0	[1]					33,233			0			0			0
Remeasurement of redemption value of convertible preferred stock		608				$ (608)			0			0			0			(608)			$ 0	[1]					0			0			608			0
Conversion of convertible preferred stock (in shares)						(42,000,592)
Conversion of convertible preferred stock						$ (216,318)			0			0			0			(216,318)
Conversion of convertible preferred stock (in shares)	[1]																				28,500,592
Conversion of convertible preferred stock		85,393																			$ 3	[1]					85,390			0			0			0
Reclassification of temporary equity to permanent equity			$ 39,307	$ 41,152			$ 0	$ 0		$ (39,307)	$ 0		$ 0	$ (1,695)		$ 0	$ 0		$ (39,307)	$ (1,695)			$ 0		$ 0			$ 39,307	$ 41,152		$ 0	$ 0		$ 0	$ 0		$ 0	$ 0
Merger and recapitalization, net of transaction costs (in shares)	[1]																				47,940,523
Merger and recapitalization, net of transaction costs		299,163																			$ 3	[1]					299,160			0			0			0
Reclassification of earn-out RSUs to earn-out shares		(581)																			0						(581)			0			0			0
Reclassification of Apex shares purchased prior to the Business Combination		(1,739)																			0	[1]					0			(1,739)			0			0
Net loss		(9,757)																			0	[1]					0			0			(9,757)			0
Net loss attributable to and accretion of redeemable noncontrolling interest						0			0			0			517			517
Net loss attributable to and accretion of redeemable noncontrolling interest		(517)																															(517)
Foreign currency translation adjustment						0			0			0			(29)			(29)
Foreign currency translation adjustment		44																			$ 0	[1]					0			0			0			44
Reclassification of share-based awards to mezzanine equity						0			(1)			0			0			(1)
Net loss attributable to and accretion of redeemable noncontrolling interest						$ 0			0			0			517			517
Balance, temporary equity, shares (in shares) at Sep. 30, 2021						0
Balance, temporary equity, including noncontrolling interest at Sep. 30, 2021		4,631				$ 0			$ 0			$ 0			$ 4,631			$ 4,631
Balance (in shares) at Sep. 30, 2021	[1]																				181,012,760
Balance at Sep. 30, 2021	[1]	$ 247,493																			$ 18						$ 614,569			$ (1,739)			$ (367,247)			$ 1,892

[1] As part of the Business Combination (as disclosed in "Note 3 — Business Combination"), all per share information has been retroactively adjusted using an exchange ratio of 8.69144 per share.