LOANS AND CREDIT QUALITY - Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Accounting Standards Update [Extensible List]			us-gaap:AccountingStandardsUpdate201613Member
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 64,294	$ 41,772
Provision for credit losses	(371)	14,655
Net (charge-offs) recoveries	124	29
Ending balance	64,047	58,299	$ 41,772
Allowance for unfunded commitments:
Beginning balance	1,588	1,065
Provision for credit losses	371	(655)
Ending balance	1,959	2,307	1,065
Total	$ 0	14,000
Cumulative Effect, Period of Adoption, Adjustment
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		1,843
Ending balance			1,843
Allowance for unfunded commitments:
Beginning balance		$ 1,897
Ending balance			$ 1,897