LONG-TERM DEBT AND FINANCING ARRANGEMENTS (Summary) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Long-term debt obligations
Long-term debt	$ 252,482	$ 268,919
Less current portion	56,057	61,930
Long-term debt, less current portion	196,425	206,989
Payments under long-term debt obligations
Due in one year or less	63,064
Due after one year through two years	82,310
Due after two years through three years	26,293
Due after three years through four years	23,276
Due after four years through five years	79,541
Total payments	274,484
Less amounts representing interest	22,002
Long-term debt	252,482	268,919
Credit Facility
Long-term debt obligations
Long-term debt	$ 70,000	70,000
Interest rate (as a percent)	3.40%
Payments under long-term debt obligations
Due in one year or less	$ 2,579
Due after one year through two years	2,895
Due after two years through three years	2,966
Due after three years through four years	2,921
Due after four years through five years	70,796
Total payments	82,157
Less amounts representing interest	12,157
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)	2.60%
Payments under long-term debt obligations
Due in one year or less	$ 1,384
Due after one year through two years	46,587
Total payments	47,971
Less amounts representing interest	2,971
Long-term debt	45,000	45,000
Notes payable
Long-term debt obligations
Long-term debt	$ 137,056	153,441
Weighted-average interest rate (as a percent)	2.70%
Payments under long-term debt obligations
Due in one year or less	$ 58,865
Due after one year through two years	32,627
Due after two years through three years	23,320
Due after three years through four years	20,349
Due after four years through five years	8,745
Total payments	143,906
Less amounts representing interest	6,850
Long-term debt	137,056	153,441
Capital lease obligations
Long-term debt obligations
Long-term debt	$ 426	478
Weighted-average interest rate (as a percent)	5.70%
Payments under long-term debt obligations
Due in one year or less	$ 236
Due after one year through two years	201
Due after two years through three years	7
Due after three years through four years	6
Total payments	450
Less amounts representing interest	24
Long-term debt	$ 426	$ 478