INVESTMENTS - (Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity) (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Available-for-sale Securities, Debt maturities, Amortized cost:
One year or less	$ 21,454
Over one through five years	137,378
Over five through ten years	144,296
Over ten years	169,998
Amortized cost	473,126
Available-for-sale Securities, Debt maturities, Fair value:
One year or less	21,573
Over one through five years	142,457
Over five through ten years	149,674
Over ten years	174,506
Amortized cost	$ 488,210

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in sixth through tenth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in second through fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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