Current and Long-Term Debt and Capital Lease Obligation, Current and Long-term Debt and Capital Lease Obligations (FY) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Unamortized debt issuance costs		$ (1,234)	$ (67)
Capital lease obligations	$ 100	246	502
Net carrying amounts	100	43,675	29,018
Less: current portion, net of unamortized debt issuance costs	(82)	(380)	(876)
Long-term debt and capital lease obligations, net of current portion and deferred financing costs	18	43,295	28,142
Secured Debt
Debt Instrument [Line Items]
Long-term debt, gross	0	44,663	5,833
Unamortized debt issuance costs	$ 0	(1,234)
Line of Credit
Debt Instrument [Line Items]
Long-term debt, gross		$ 0	$ 22,750

Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Amount of long-term debt and lease obligation, classified as current.

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