Business Combination - Elements of Business Combination (Q3) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020
Reverse Recapitalization [Abstract]
Cash - Silver Spike trust and cash, net of redemptions		$ 254,203
Cash - PIPE Financing		325,000
Less: cash consideration paid to Legacy WMH equity holders		(455,182)
Less: transaction costs and advisory fees		(44,052)
Net proceeds from the Business Combination		79,969	$ 0
Less: initial fair value of warrant liability recognized in the Business Combination		(193,978)	0
Add: transaction costs allocated to Warrants	$ 5,500	5,547
Add: non-cash assets assumed from Silver Spike		1,053	0
Add: deferred tax asset		147,973	0
Less: tax receivable agreement liability		(126,150)	$ 0
Net adjustment to total equity from the Business Combination		$ (85,586)

The net book value of a nonmonetary asset transferred or exchanged in connection with the acquisition of a business or asset in a noncash transaction. Noncash is defined as transactions during a period that affect recognized assets or liabilities but that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period. Nonmonetary assets and liabilities are assets and liabilities that will not result in cash receipts or cash payments in the future.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=123431023&loc=d3e4332-108586

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=123431023&loc=d3e4304-108586

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=123431023&loc=d3e4313-108586

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