FAIR VALUE MEASUREMENTS (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	9 Months Ended
	Oct. 31, 2019	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Fair value measurements
Purchase of other investments			$ 10,285	$ 3,000
Other Assets
Fair value measurements
Acquired additional securities			200
Loss on equity securities			2,100
Carrying Value
Fair value measurements
Long-term debt		$ 88,300	88,300		$ 91,000
Carrying Value | Other Assets
Fair value measurements
Strategic investments		21,200	21,200		23,100
Short Term Investments and Commercial Paper
Fair value measurements
Equity investments		200	200		200
Other investments
Fair value measurements
Purchase of other investments			10,000
Other investments | Renewable energy partnership
Fair value measurements
Investment cost		14,400	14,400
Purchase of other investments	$ 14,100	300
Investment Tax Credit		12,000
Equity investments		2,400	2,400
Interest rate swap | Other Assets
Fair value measurements
Unrealized loss			200
Level 2 | Estimated Fair Value
Fair value measurements
Long-term debt		88,800	88,800		91,600
Level 3
Fair value measurements
Payments to acquire investments			12,400
Unrealized loss			0
Recurring basis
Fair value measurements
Total assets and liabilities measured at fair value		18,094	18,094		17,151
Recurring basis | Certificate of deposit
Fair value measurements
Cash and cash equivalents		3,380	3,380		380
Recurring basis | Money market funds
Fair value measurements
Cash and cash equivalents		2,151	2,151		2,266
Recurring basis | Short Term Investments
Fair value measurements
Investments		250	250		393
Recurring basis | Commercial paper
Fair value measurements
Investments					13,972
Recurring basis | Other investments
Fair value measurements
Investments		12,394	12,394
Recurring basis | Interest rate swap
Fair value measurements
Derivative assets					140
Derivative liabilities		(81)	(81)
Recurring basis | Level 1
Fair value measurements
Total assets and liabilities measured at fair value		2,401	2,401		2,659
Recurring basis | Level 1 | Money market funds
Fair value measurements
Cash and cash equivalents		2,151	2,151		2,266
Recurring basis | Level 1 | Short Term Investments
Fair value measurements
Investments		250	250		393
Recurring basis | Level 2
Fair value measurements
Total assets and liabilities measured at fair value		3,299	3,299		14,492
Recurring basis | Level 2 | Certificate of deposit
Fair value measurements
Cash and cash equivalents		3,380	3,380		380
Recurring basis | Level 2 | Commercial paper
Fair value measurements
Investments					13,972
Recurring basis | Level 2 | Interest rate swap
Fair value measurements
Derivative assets					$ 140
Derivative liabilities		(81)	(81)
Recurring basis | Level 3
Fair value measurements
Total assets and liabilities measured at fair value		12,394	12,394
Recurring basis | Level 3 | Other investments
Fair value measurements
Investments		$ 12,394	$ 12,394