LONG-TERM DEBT AND FINANCING ARRANGEMENTS (Summary) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Long-term debt obligations
Long-term debt	$ 249,632	$ 268,919
Less current portion	51,562	61,930
Long-term debt, less current portion	198,070	206,989
Payments under long-term debt obligations
Due in one year or less	59,036
Due after one year through two years	80,391
Due after two years through three years	29,575
Due after three years through four years	25,258
Due after four years through five years	77,443
Due after five years	225
Total payments	271,928
Less amounts representing interest	22,296
Long-term debt	249,632	268,919
Credit Facility
Long-term debt obligations
Long-term debt	$ 70,000	70,000
Interest rate (as a percent)	3.60%
Payments under long-term debt obligations
Due in one year or less	$ 2,771
Due after one year through two years	3,069
Due after two years through three years	3,097
Due after three years through four years	3,076
Due after four years through five years	70,050
Total payments	82,063
Less amounts representing interest	12,063
Long-term debt	70,000	70,000
Credit Facility | Interest rate swap agreement
Long-term debt obligations
Amount of borrowings covered by the interest rate swap	$ 50,000
Effective fixed interest rate on hedged borrowings (as a percent)	3.35%
Accounts receivable securitization program
Long-term debt obligations
Long-term debt	$ 45,000	45,000
Interest rate (as a percent)	2.90%
Payments under long-term debt obligations
Due in one year or less	$ 1,507
Due after one year through two years	46,271
Total payments	47,778
Less amounts representing interest	2,778
Long-term debt	45,000	45,000
Notes payable
Long-term debt obligations
Long-term debt	$ 134,258	153,441
Weighted-average interest rate (as a percent)	2.90%
Payments under long-term debt obligations
Due in one year or less	$ 54,521
Due after one year through two years	30,908
Due after two years through three years	26,471
Due after three years through four years	22,177
Due after four years through five years	7,393
Due after five years	225
Total payments	141,695
Less amounts representing interest	7,437
Long-term debt	134,258	153,441
Capital lease obligations
Long-term debt obligations
Long-term debt	$ 374	478
Weighted-average interest rate (as a percent)	5.60%
Payments under long-term debt obligations
Due in one year or less	$ 237
Due after one year through two years	143
Due after two years through three years	7
Due after three years through four years	5
Total payments	392
Less amounts representing interest	18
Long-term debt	$ 374	$ 478