NOTES PAYABLE AND AMENDED CREDIT AGREEMENT - Summary of Notes Payable and Credit Agreement (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2018	Dec. 31, 2017
Debt Instruments [Abstract]
Payments/Long term debt, Total	$ 61,424	$ 60,772
Less current portion	(4,817)	(4,044)
Long term portion	56,607	56,728
Credit Facility [Member]
Debt Instruments [Abstract]
Payments/Long term debt, Total	$ 56,000	54,000
Average effective interest rate	3.80%
3.25% through 4.75% Notes Payable due in Next Year [Member]
Debt Instruments [Abstract]
Payments/Long term debt, Total	$ 5,424	$ 6,772
Annual installments	$ 4,817
3.25% through 4.75% Notes Payable due in Next Year [Member] \| Minimum [Member]
Debt Instruments [Abstract]
Percentage of interest accrued	3.25%
3.25% through 4.75% Notes Payable due in Next Year [Member] \| Maximum [Member]
Debt Instruments [Abstract]
Percentage of interest accrued	4.75%

Amount of the total principal payments made during the annual reporting period.

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Contractual interest rate for funds borrowed, under the debt agreement.

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The effective interest rate during the reporting period.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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