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Stockholders' Equity - Performance-Based Restricted Stock Units (PSUs) (Details)	1 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended
	Feb. 28, 2021 installment shares	Mar. 31, 2020 shares	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) shares	Sep. 30, 2020 USD ($)	Dec. 31, 2020 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Modification expense | $			$ 2,400,000	$ 400,000	$ 3,700,000	$ 400,000
PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares) | shares					71,000		75,828
Shares issued for each PSU, ratio	1	1
Award vesting percentage		25.00%
Actual performance percentage							172.00%
Shares cancelled (in shares) | shares					12,000		12,090
Stock-based compensation expense | $			(500,000)	$ 0	$ 3,800,000	0
Unrecognized stock-based compensation cost | $			4,700,000		$ 4,700,000
Weighted-average period of recognition					2 years 8 months 12 days
PSUs | Performance Target One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Target performance percentage	90.00%	90.00%
Award vesting percentage	50.00%	50.00%
PSUs | Performance Target Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Target performance percentage	100.00%	100.00%
Award vesting percentage	100.00%	100.00%
PSUs | Performance Target Three
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Target performance percentage	110.00%	110.00%
Award vesting percentage	150.00%	200.00%
PSUs | First Installment
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage	25.00%
PSUs | Remaining Installments
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage	6.25%
Number of vesting installments | installment	12
PSUs | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares) | shares	70,680	87,918
Target performance percentage	150.00%	200.00%
Revest Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares cancelled (in shares) | shares					0
Unrecognized stock-based compensation cost | $			43,900,000		$ 43,900,000
Weighted-average period of recognition					1 year
Vesting of restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares) | shares					1,890,000
Shares cancelled (in shares) | shares					470,000
Unrecognized stock-based compensation cost | $			176,600,000		$ 176,600,000
Modification expense | $			$ 3,900,000		$ 3,900,000	$ 4,800,000
Weighted-average period of recognition					2 years 8 months 12 days
Vesting of restricted stock units | Performance Target One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage					25.00%

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