LONG-TERM OBLIGATIONS - Fees and Rates Under Credit Facilities (Details)	6 Months Ended
	Jun. 30, 2018
Consolidated Leverage Ratio: Greater Than 3.00 to 1.0
Line of Credit Facility [Line Items]
Commitment fee percentage	0.35%
Letter Of Credit Fee	2.00%
Consolidated Leverage Ratio: Greater Than 3.00 to 1.0 | Eurodollar [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.25%
Consolidated Leverage Ratio: Greater Than 3.00 to 1.0 | Base Rate [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.25%
Consolidated Leverage Ratio: Less Than Equal To 3.00 to 1.0 but Greater Than 2.00 to 1.0
Line of Credit Facility [Line Items]
Commitment fee percentage	0.30%
Letter Of Credit Fee	1.75%
Consolidated Leverage Ratio: Less Than Equal To 3.00 to 1.0 but Greater Than 2.00 to 1.0 | Eurodollar [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.00%
Consolidated Leverage Ratio: Less Than Equal To 3.00 to 1.0 but Greater Than 2.00 to 1.0 | Base Rate [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.00%
Consolidated Leverage Ratio: Less Than Equal to 2.00 to 1.0 but Greater Than 1.00 to 1.0
Line of Credit Facility [Line Items]
Commitment fee percentage	0.25%
Letter Of Credit Fee	1.50%
Consolidated Leverage Ratio: Less Than Equal to 2.00 to 1.0 but Greater Than 1.00 to 1.0 | Eurodollar [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.75%
Consolidated Leverage Ratio: Less Than Equal to 2.00 to 1.0 but Greater Than 1.00 to 1.0 | Base Rate [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.75%
Consolidated Leverage Ratio: Less Than Equal to 1.00 to 1.0
Line of Credit Facility [Line Items]
Commitment fee percentage	0.20%
Letter Of Credit Fee	1.25%
Consolidated Leverage Ratio: Less Than Equal to 1.00 to 1.0 | Eurodollar [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.50%
Consolidated Leverage Ratio: Less Than Equal to 1.00 to 1.0 | Base Rate [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.50%
Minimum [Member] | Consolidated Leverage Ratio: Greater Than 3.00 to 1.0
Line of Credit Facility [Line Items]
Consolidated Leverage Ratio	3.00
Minimum [Member] | Consolidated Leverage Ratio: Less Than Equal To 3.00 to 1.0 but Greater Than 2.00 to 1.0
Line of Credit Facility [Line Items]
Consolidated Leverage Ratio	2.00
Minimum [Member] | Consolidated Leverage Ratio: Less Than Equal to 2.00 to 1.0 but Greater Than 1.00 to 1.0
Line of Credit Facility [Line Items]
Consolidated Leverage Ratio	1.00
Maximum [Member] | Consolidated Leverage Ratio: Less Than Equal To 3.00 to 1.0 but Greater Than 2.00 to 1.0
Line of Credit Facility [Line Items]
Consolidated Leverage Ratio	3.00
Maximum [Member] | Consolidated Leverage Ratio: Less Than Equal to 2.00 to 1.0 but Greater Than 1.00 to 1.0
Line of Credit Facility [Line Items]
Consolidated Leverage Ratio	2.00
Maximum [Member] | Consolidated Leverage Ratio: Less Than Equal to 1.00 to 1.0
Line of Credit Facility [Line Items]
Consolidated Leverage Ratio	1.00