MARKETABLE SECURITIES - Contractual Maturities of Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Amortized Cost
Due within one year	$ 3,478
Due after one year through five years	52,628
Due after five years through ten years	48,675
Due after ten years	78,220
Available-for-sale debt securities, amortized cost basis	351,130	$ 210,212
Estimated Fair Value
Due within one year	3,509
Due after one year through five years	55,426
Due after five years through ten years	52,451
Due after ten years	83,801
Available-for-sale debt securities, estimated fair value	368,887	212,716
Mortgage-backed securities
Amortized Cost
Available-for-sale debt securities, amortized cost basis	95,415
Available-for-sale debt securities, amortized cost basis	95,415	83,967
Estimated Fair Value
Available-for-sale debt securities, estimated fair value	98,371
Available-for-sale debt securities, estimated fair value	98,371	84,182
Collateralized mortgage obligations
Amortized Cost
Available-for-sale debt securities, amortized cost basis	72,714
Available-for-sale debt securities, amortized cost basis	72,714	89,798
Estimated Fair Value
Available-for-sale debt securities, estimated fair value	75,329
Available-for-sale debt securities, estimated fair value	$ 75,329	$ 90,927

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121558606&loc=SL82898722-210454

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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