SENIOR NOTES PAYABLE AND OTHER DEBT - Indebtedness of Maturities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Scheduled maturities of borrowing arrangements and other provisions excluding capital lease obligations
2019	$ 650,615
2020	613,759
2021	313,368
2022	1,545,289
2023	1,459,826
Thereafter	5,764,046
Total maturities	10,346,903
Long-term debt and short-term borrowings, gross	10,346,903	$ 10,829,702
Line of Credit Facility and Commercial Paper Program amount outstanding	415,300
Unrestricted cash and cash equivalents	81,987	$ 72,277
Unsecured Revolving Credit Facility and Commercial Paper
Scheduled maturities of borrowing arrangements and other provisions excluding capital lease obligations
2019	270,000
2020	0
2021	227,323
2022	0
2023	0
Thereafter	0
Total maturities	497,323
Principal Amount Due at Maturity
Scheduled maturities of borrowing arrangements and other provisions excluding capital lease obligations
2019	372,495
2020	598,436
2021	71,813
2022	1,532,545
2023	1,450,721
Thereafter	5,683,902
Total maturities	9,709,912
Scheduled Periodic Amortization
Scheduled maturities of borrowing arrangements and other provisions excluding capital lease obligations
2019	8,120
2020	15,323
2021	14,232
2022	12,744
2023	9,105
Thereafter	80,144
Total maturities	$ 139,668