FINANCING RECEIVABLES - Summary of Financing Receivables (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total financing receivables with contractual maturities of one year or less	$ 74	$ 121
Less: allowance for expected credit losses	(879)	(722)	$ (1,489)
Total financing receivables	11,752	13,719
Total Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total uninvoiced client financing receivables of clients with no related trade accounts receivable	1,276	864
Total Past Due | Trade Accounts Receivable
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total uninvoiced client financing receivables of clients with no related trade accounts receivable	7,453	9,815
Uninvoiced client financing receivables related to trade accounts receivable that are 1 to 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total uninvoiced client financing receivables of clients with no related trade accounts receivable	771	713
Uninvoiced client financing receivables related to trade accounts receivable that are 1 to 90 Days Past Due | Trade Accounts Receivable
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total uninvoiced client financing receivables of clients with no related trade accounts receivable	6,555	9,100
Uninvoiced client financing receivables related to trade accounts receivable that are 91 to 180 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total uninvoiced client financing receivables of clients with no related trade accounts receivable	382	78
Uninvoiced client financing receivables related to trade accounts receivable that are 91 to 180 Days Past Due | Trade Accounts Receivable
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total uninvoiced client financing receivables of clients with no related trade accounts receivable	556	329
Uninvoiced client financing receivables related to trade accounts receivable that are 181 + Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total uninvoiced client financing receivables of clients with no related trade accounts receivable	123	73
Uninvoiced client financing receivables related to trade accounts receivable that are 181 + Days Past Due | Trade Accounts Receivable
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total uninvoiced client financing receivables of clients with no related trade accounts receivable	342	386
Total Not Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total uninvoiced client financing receivables of clients with no related trade accounts receivable	$ 5,104	$ 4,505