SENIOR NOTES PAYABLE AND OTHER DEBT - Indebtedness of Maturities (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Scheduled maturities of borrowing arrangements and other provisions excluding capital lease obligations
2017	$ 628,874
2018	1,293,816
2019	1,711,920
2020	1,428,722
2021	783,163
Thereafter	6,174,063
Total maturities	12,020,558	$ 11,190,914
Unrestricted cash and cash equivalents	91,284	286,707	$ 51,701	$ 53,023
Amount outstanding, net of cash and cash equivalents	79,400
Principal Amount Due at Maturity
Scheduled maturities of borrowing arrangements and other provisions excluding capital lease obligations
2017	609,499
2018	1,101,879
2019	1,697,131
2020	1,416,913
2021	772,838
Thereafter	6,056,092
Total maturities	11,654,352
Unsecured Revolving Credit Facility
Scheduled maturities of borrowing arrangements and other provisions excluding capital lease obligations
2017	0
2018	170,731
2019	0
2020	0
2021	0
Thereafter	0
Total maturities	170,731	$ 146,538
Scheduled Periodic Amortization
Scheduled maturities of borrowing arrangements and other provisions excluding capital lease obligations
2017	19,375
2018	21,206
2019	14,789
2020	11,809
2021	10,325
Thereafter	117,971
Total maturities	195,475
Senior Notes | 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 | 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	$ 23,000
Interest rate	6.59%