REVENUE RECOGNITION AND RECEIVABLES - Accounts Receivable (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Accounts Receivable
Gross accounts receivable	$ 129,700	$ 131,400
Allowance for credit loss	15,000	13,900
Retained earnings	470,056	475,887
Customer receivable, current	4,336	4,145
Customer receivable - long term	40,206	39,652
FirstNet agreement
Accounts Receivable
Customer receivable	44,500	43,800
Customer receivable, current	4,300	4,100
Customer receivable - long term	$ 40,200	$ 39,700