Summary of Significant Accounting Policies - Narrative (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2022 USD ($) segment	Mar. 31, 2021 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
New Accounting Pronouncements or Change in Accounting Principle
Provision for expected credit losses	$ 195	$ (1,600)	$ (3,592)
Guaranty liabilities	$ 26,184		25,989	$ 29,581
Number of operating segments | segment	1
Revenues	$ 678,247	503,980
Commercial mortgage origination, net
New Accounting Pronouncements or Change in Accounting Principle
Revenues	94,062	67,251
Revision of Prior Period, Reclassification, Adjustment | Commercial mortgage origination, net
New Accounting Pronouncements or Change in Accounting Principle
Revenues	19,900
Accounts Receivable
New Accounting Pronouncements or Change in Accounting Principle
Provision for expected credit losses	1,900	$ 300
Allowance for doubtful accounts	$ 18,600		16,700
Loans Receivable
New Accounting Pronouncements or Change in Accounting Principle
Allowance for credit loss			$ 3,800