INVESTMENT SECURITIES - Maturities of Equity Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt and Equity Securities, FV-NI [Line Items]
Equity securities amortized cost	$ 41,452	$ 18,810
Equity securities at fair value	41,452	18,810
Money market mutual funds
Debt and Equity Securities, FV-NI [Line Items]
Equity securities, within one year, amortized cost	41,452
Equity securities, within one year, fair value	$ 41,452
Equity securities, within one year, weighted average yield	0.40%
Equity securities, after one, but within five years, amortized cost	$ 0
Equity securities, after one, but within five years, fair value	$ 0
Equity securities, after one, but within five years, weighted average yield	0.00%
Equity securities, after five, but within ten years, amortized cost	$ 0
Equity securities, after five, but within ten years, fair value	$ 0
Equity securities, after five, but within ten years, weighted average yield	0.00%
Equity securities, greater than ten years, amortized cost	$ 0
Equity securities, greater than ten years, fair value	$ 0
Equity securities, greater than ten years, weighted average yield	0.00%
Equity securities amortized cost	$ 41,452	18,810
Equity securities at fair value	$ 41,452	$ 18,810
Equity securities, weighted average yield	0.40%