CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
CURRENT ASSETS:
Accounts receivable, allowance	$ 26,303	$ 25,174
PROPERTY, EQUIPMENT AND FACILITIES - accumulated depreciation and amortization	152,217	176,300
OTHER ASSETS:
Noncurrent receivables, allowance	$ 4,789	$ 3,465
STOCKHOLDERS' EQUITY:
Common stock, par value (in dollars per share)	$ 0	$ 0
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares issued (in shares)	26,978,432	26,476,329
Common stock, shares outstanding (in shares)	26,978,432	26,476,329
Treasury stock, shares (in shares)	5,910,541	5,910,541
Series A Convertible Preferred Stock [Member]
SERIES A CONVERTIBLE PREFERRED STOCK
Preferred stock, par value (in dollars per share)	$ 0	$ 0
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	12,700	12,700
Preferred stock, shares outstanding (in shares)	12,700	12,700