ACCOUNTS RECEIVABLE, NET OF ALLOWANCE - Activity in Allowance for Doubtful Accounts (Detail) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Allowance for Doubtful Accounts Receivable [Roll Forward]
Provision for doubtful accounts	$ 5,074	$ 4,529
Balance, end of period	5,747		$ 5,711
Contract Cancellations
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance, beginning of period	5,892		5,884
Provision for doubtful accounts	5,074		6,275
Charge-offs, net	(5,219)		(6,267)
Amounts related to assets held for sale			(181)
Balance, end of period	$ 5,747		$ 5,711