MARKETABLE SECURITIES - Contractual Maturities of Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Amortized Cost
Due within one year	$ 1,015
Due after one year through five years	13,407
Due after five years through ten years	13,324
Due after ten years	8,701
Available-for-sale debt securities, amortized cost basis	210,212	$ 239,945
Estimated Fair Value
Due within one year	1,019
Due after one year through five years	13,772
Due after five years through ten years	13,924
Due after ten years	8,892
Available-for-sale debt securities, estimated fair value	212,716	232,975
Amortized Cost
Due within one year	2,189
Due after one year through five years	30,221
Due after five years through ten years	32,771
Due after ten years	73,235
Amortized Cost	155,458	163,164
Estimated Fair Value
Due within one year	2,200
Due after one year through five years	31,179
Due after five years through ten years	34,078
Due after ten years	75,666
Held-to-maturity securities, estimated fair value	160,460	162,800
Mortgage-backed securities
Amortized Cost
Available-for-sale securities without single maturity date	83,967
Available-for-sale debt securities, amortized cost basis	83,967	93,083
Estimated Fair Value
Available-for-sale securities without single maturity date	84,182
Available-for-sale debt securities, estimated fair value	84,182	89,459
Amortized Cost
Held-to-maturity securities, without single maturity date	14,365
Amortized Cost	14,365	17,163
Estimated Fair Value
Held-to-maturity securities, without single maturity date	14,550
Held-to-maturity securities, estimated fair value	14,550	16,717
Collateralized mortgage obligations
Amortized Cost
Available-for-sale securities without single maturity date	89,798
Available-for-sale debt securities, amortized cost basis	89,798	111,341
Estimated Fair Value
Available-for-sale securities without single maturity date	90,927
Available-for-sale debt securities, estimated fair value	90,927	108,969
Amortized Cost
Held-to-maturity securities, without single maturity date	2,677
Amortized Cost	2,677	4,059
Estimated Fair Value
Held-to-maturity securities, without single maturity date	2,787
Held-to-maturity securities, estimated fair value	$ 2,787	$ 4,079