UNSECURED SENIOR NOTES (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)
Mortgage loans and Notes payable
Less: Loan procurement costs, net	$ (2,313)	$ (2,800)
Total unsecured senior notes, net	1,038,728	741,904
Senior Notes
Mortgage loans and Notes payable
Carrying value	1,050,000	750,000
Less: Discount on issuance of notes, net	(4,099)	(2,888)
Less: Loan procurement costs, net	(7,173)	(5,208)
Total unsecured senior notes, net	$ 1,038,728	741,904
Senior Notes | Maximum
Mortgage loans and Notes payable
Consolidated leverage ratio	0.60
Secured debt leverage ratio	0.40
Senior Notes | Minimum
Mortgage loans and Notes payable
Consolidated interest coverage ratio	1.50
Financial and customary covenant, minimum unencumbered asset (as a percent)	150.00%
Senior notes 4.800% due 2022
Mortgage loans and Notes payable
Senior notes, principal amount	$ 250,000	$ 250,000
Interest rate (as a percent)	4.80%	4.80%
Carrying value	$ 250,000	$ 250,000
Effective interest rate of senior notes (as a percent)	4.82%
Senior notes 4.375% due 2023
Mortgage loans and Notes payable
Senior notes, principal amount	$ 250,000	$ 250,000
Interest rate (as a percent)	4.375%	4.375%
Carrying value	$ 250,000	$ 250,000
Effective interest rate of senior notes (as a percent)	4.50%
Senior notes 4.000% due 2025
Mortgage loans and Notes payable
Senior notes, principal amount	$ 250,000	$ 250,000
Interest rate (as a percent)	4.00%	4.00%
Carrying value	$ 250,000	$ 250,000
Effective interest rate of senior notes (as a percent)	4.03%
Senior Notes 3.125% Due 2026
Mortgage loans and Notes payable
Senior notes, principal amount	$ 300,000
Interest rate (as a percent)	3.125%
Carrying value	$ 300,000
Effective interest rate of senior notes (as a percent)	3.18%