SENIOR NOTES PAYABLE AND OTHER DEBT - Indebtedness of Maturities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Scheduled maturities of borrowing arrangements and other provisions excluding capital lease obligations
2018	$ 5,154
2019	553,880
2020	598,357
2021	590,124
2022	1,487,134
Thereafter	7,349,351
Total maturities	10,584,000	$ 11,365,633
Unrestricted cash and cash equivalents	86,107	81,355
Revolving credit facility borrowings outstanding, net of cash and cash equivalents	428,200
Principal Amount Due at Maturity
Scheduled maturities of borrowing arrangements and other provisions excluding capital lease obligations
2018	0
2019	538,766
2020	583,866
2021	62,406
2022	1,475,293
Thereafter	7,262,876
Total maturities	9,923,207
Unsecured Revolving Credit Facility
Scheduled maturities of borrowing arrangements and other provisions excluding capital lease obligations
2018	0
2019	0
2020	0
2021	514,353
2022	0
Thereafter	0
Total maturities	514,353	$ 535,832
Scheduled Periodic Amortization
Scheduled maturities of borrowing arrangements and other provisions excluding capital lease obligations
2018	5,154
2019	15,114
2020	14,491
2021	13,365
2022	11,841
Thereafter	86,475
Total maturities	146,440
Senior Notes Included in Thereafter Maturities | 6.90% Senior Notes due 2037, subject to repurchase at option of holders
Scheduled maturities of borrowing arrangements and other provisions excluding capital lease obligations
Total maturities	$ 52,400
Interest rate	6.90%
Senior Notes Included in Thereafter Maturities | 6.59% Senior Notes due 2038, subject to repurchase at option of holders
Scheduled maturities of borrowing arrangements and other provisions excluding capital lease obligations
Total maturities	$ 22,800
Interest rate	6.59%