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EMPLOYEE BENEFIT PLANS - Plan assets using fair value hierarchy (Details) - Retirement Income Plan - USD ($) $ in Thousands | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Total |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Investments measured at Net Asset Value |  | $ 638 | $ 691
Investments at Fair Value |  | 6,802 | 6,722
Cash and Cash Equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets in the Fair Value Hierarchy | [1] | 202 | 192
Cash and Cash Equivalents | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets in the Fair Value Hierarchy | [1] | 202 | 192
Cash and Cash Equivalents | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets in the Fair Value Hierarchy | [1] | 0 | 0
Fixed Income Securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets in the Fair Value Hierarchy | [2] | 1,979 | 1,601
Fixed Income Securities | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets in the Fair Value Hierarchy | [2] | 0 | 0
Fixed Income Securities | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets in the Fair Value Hierarchy | [2] | 1,979 | 1,601
Domestic Equity Securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets in the Fair Value Hierarchy | [3] | 2,693 | 2,844
Domestic Equity Securities | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets in the Fair Value Hierarchy | [3] | 993 | 1,047
Domestic Equity Securities | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets in the Fair Value Hierarchy | [3] | 1,700 | 1,797
International Equity Securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets in the Fair Value Hierarchy | [4] | 1,290 | 1,394
International Equity Securities | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets in the Fair Value Hierarchy | [4] | 0 | 0
International Equity Securities | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets in the Fair Value Hierarchy | [4] | 1,290 | 1,394
Investment | Total |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets in the Fair Value Hierarchy |  | 6,164 | 6,031
Investment | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets in the Fair Value Hierarchy |  | 1,195 | 1,239
Investment | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets in the Fair Value Hierarchy |  | $ 4,969 | $ 4,792
[1] | Cash and cash equivalents, which are used to pay benefits and plan administrative expenses, are held in Rule 2a-7 money market funds.
[2] | Fixed income securities are primarily valued using a market approach with inputs that include broker quotes, benchmark yields, base spreads and reported trades.
[3] | Domestic equity securities are valued using a market approach based on the quoted market prices of identical instruments in their respective markets.
[4] | International equity securities are valued using a market approach based on the quoted market prices of identical instruments in their respective markets.

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- Definition Fair value of investment other than investment in equity security, investment in debt security and equity method investment. Includes, but is not limited to, investment in certain entities that calculate net asset value per share. Example includes, but is not limited to, investment in hedge fund, venture capital fund, private equity fund, and real estate partnership or fund. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 6A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=99377789&loc=SL6742756-110258 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 35 -Paragraph 54B -URI http://asc.fasb.org/extlink&oid=99392525&loc=SL7495116-110257 + Details
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