Share-Based Compensation - Activity of Service Period Based and Performance Based Stock Options (Details) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021 USD ($) $ / shares shares	Dec. 31, 2020 shares
Stock Option Activity, Additional Disclosures
Share price (in dollars per share)	$ 6.27
Service period based stock options
Number of Options
Options Outstanding Beginning Balance (in shares) | shares	10,833
Options Granted (in shares) | shares	1,527
Options Exercised (in shares) | shares	(2,114)
Options Forfeited (in shares) | shares	(747)
Options Outstanding Ending Balance (in shares) | shares	9,499	10,833
Weighted Average Exercise Price
Options Outstanding Beginning Balance (in dollars per share)	$ 3.96
Options Granted (in dollars per share)	9.08
Options Exercised (in dollars per share)	4.35
Options Forfeited (in dollars per share)	4.49
Options Outstanding Ending Balance (in dollars per share)	$ 4.66
Stock Option Activity, Additional Disclosures
Options Exercisable (in shares) | shares	6,372
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 3.71
Weighted Average Remaining Contractual Term, Options Outstanding Beginning Balance		6 years 9 months 18 days
Weighted Average Remaining Contractual Term, Options Outstanding Ending Balance	6 years 8 months 12 days
Weighted Average Remaining Contractual Term, Options Exercisable	5 years 6 months
Aggregate Intrinsic Value, Options Exercised | $	$ 13,236
Aggregate Intrinsic Value, Options Outstanding Ending Balance | $	19,690
Aggregate Intrinsic Value, Options Exercisable | $	$ 16,367
Performance based stock options
Number of Options
Options Outstanding Beginning Balance (in shares) | shares	81
Options Granted (in shares) | shares	0
Options Exercised (in shares) | shares	(40)
Options Forfeited (in shares) | shares	0
Options Outstanding Ending Balance (in shares) | shares	41	81
Weighted Average Exercise Price
Options Outstanding Beginning Balance (in dollars per share)	$ 4.34
Options Granted (in dollars per share)	0
Options Exercised (in dollars per share)	4.34
Options Forfeited (in dollars per share)	0
Options Outstanding Ending Balance (in dollars per share)	$ 4.34
Stock Option Activity, Additional Disclosures
Options Exercisable (in shares) | shares	41
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 4.34
Weighted Average Remaining Contractual Term, Options Outstanding Beginning Balance		3 years 1 month 6 days
Weighted Average Remaining Contractual Term, Options Outstanding Ending Balance	2 years 3 months 18 days
Weighted Average Remaining Contractual Term, Options Exercisable	2 years 3 months 18 days
Aggregate Intrinsic Value, Options Exercised | $	$ 401
Aggregate Intrinsic Value, Options Outstanding Ending Balance | $	79
Aggregate Intrinsic Value, Options Exercisable | $	$ 79