Condensed Consolidated Balance Sheets (Q3) (Parenthetical) - $ / shares	Sep. 30, 2021	Jan. 12, 2021	Dec. 31, 2020	Dec. 31, 2019
Preferred stock, par value (in USD per share)	$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (shares)	10,000,000		10,000,000	10,000,000
Preferred stock, shares issued (shares)	0		0	0
Preferred stock, shares outstanding (shares)	0		0	0
Common stock, par value (USD per share)		$ 0.0001
Common stock, shares outstanding (shares)		145,266,000
Common Class I
Common stock, par value (USD per share)	$ 0.0001		$ 0.0001
Common stock, shares authorized (shares)	538,000,000		538,000,000
Common stock, shares issued (shares)	153,391,000		92,760,000
Common stock, shares outstanding (shares)	153,391,000	138,728,373	92,760,000
Common Class 2
Common stock, par value (USD per share)	$ 0.0001	$ 0.0001	$ 0.0001
Common stock, shares authorized (shares)	27,000,000		27,000,000
Common stock, shares issued (shares)	5,223,000		8,197,000
Common stock, shares outstanding (shares)	5,223,000	6,537,735	8,197,000

Face amount or stated value per share of common stock.

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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Face amount or stated value per share of preferred stock nonredeemable or redeemable solely at the option of the issuer.

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Total number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) issued to shareholders (includes related preferred shares that were issued, repurchased, and remain in the treasury). May be all or portion of the number of preferred shares authorized. Excludes preferred shares that are classified as debt.

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