LEASES - Lessee Future Minimum Payments (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) lease community	Sep. 30, 2019
Lessee operating leases
Number of communities subject to ground leases | community	6
Operating leases existence of option to extend	true
Lease classification per practical expedient	true
Operating lease right-of-use assets	$ 204,225
Weighted average remaining lease term		44 years 8 months 12 days
Weighted average discount rate	5.00%
Increase in operating lease right-to-use assets	$ 111,055
Number of ground leases that became fixed | lease	2
Future minimum lease payments
Operating lease liabilities	$ 198,558
LAND
Future minimum lease payments
2020	12,442
2021	12,442
2022	12,442
2023	12,442
2024	12,442
Thereafter	455,221
Total future minimum lease payments (undiscounted)	517,431
Difference between future undiscounted cash flows and discounted cash flows	(318,873)
Operating lease liabilities	$ 198,558