MARKETABLE SECURITIES - Narrative (Details)	3 Months Ended	9 Months Ended
Sep. 30, 2018 USD ($) security position	Sep. 30, 2018 USD ($) security position	Sep. 30, 2017 security	Dec. 31, 2017 USD ($)
Investments, Debt and Equity Securities [Abstract]
Other than temporary impairment losses on debt securities related to credit losses	$ 0	$ 0		$ 0
Number of investment positions in an unrealized loss position \| position	203	203
Fair value of securities pledged as collateral	$ 233,559,000	$ 233,559,000		$ 245,600,000
Number of held-to-maturity securities sold \| security	0	0	3

The cumulative amount of credit losses recognized in earnings related to debt securities held for which a portion of an other than temporary impairment (OTTI) was recognized in other comprehensive income (a component of shareholders' equity).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 8B
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=SL6284393-111563

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 8B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=SL6284393-111563

Name:	us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCreditLossesOnDebtSecuritiesHeld
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant