SENIOR NOTES PAYABLE AND OTHER DEBT - Indebtedness of Maturities (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Feb. 29, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Scheduled maturities of borrowing arrangements and other provisions excluding capital lease obligations
2016	$ 607,779
2017	772,197
2018	1,446,988
2019	1,820,554
2020	1,428,035
Thereafter	5,234,473
Total maturities	11,310,026		$ 11,271,020
Unrestricted cash and cash equivalents	51,701		53,023	$ 120,225	$ 55,348
Amount outstanding, net of cash and cash equivalents	272,800
Interest rate (as a percent)		1.132%
Principal Amount Due at Maturity
Scheduled maturities of borrowing arrangements and other provisions excluding capital lease obligations
2016	586,002
2017	746,458
2018	1,101,879
2019	1,806,428
2020	1,416,913
Thereafter	5,108,858
Total maturities	10,766,538
Unsecured Revolving Credit Facility
Scheduled maturities of borrowing arrangements and other provisions excluding capital lease obligations
2016	0
2017	0
2018	324,488
2019	0
2020	0
Thereafter	0
Total maturities	324,488		180,683
Scheduled Periodic Amortization
Scheduled maturities of borrowing arrangements and other provisions excluding capital lease obligations
2016	21,777
2017	25,739
2018	20,621
2019	14,126
2020	11,122
Thereafter	125,615
Total maturities	219,000
Mortgage Loans Held-for-Sale
Scheduled maturities of borrowing arrangements and other provisions excluding capital lease obligations
Total maturities	11,100		$ 22,900
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 (as a percent)	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 (as a percent)	6.59%