REVOLVING CREDIT FACILITY AND UNSECURED TERM LOANS (Details) - USD ($) $ in Thousands					1 Months Ended	9 Months Ended
	Jun. 19, 2019	Apr. 04, 2017	Oct. 26, 2015	Dec. 17, 2013	Jan. 31, 2019	Sep. 30, 2020	Dec. 31, 2019	Apr. 22, 2015	Jun. 20, 2011
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS
Loan procurement costs, net of amortization						$ 3,382	$ 4,059
Less: Loan procurement costs, net						(3,382)	(4,059)
Term Loan
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS
Write off of unamortized cost	$ 100
Revolver
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS
Remaining borrowing capacity						712,000
Outstanding letter of credit						$ 700
Effective weighted average interest rate (as a percent)						1.25%
Term Loan Facility | Term Loan B
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS
Maximum borrowing capacity									$ 100,000
Credit Facility
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS
Loan procurement costs capitalized	3,900
Repayment of outstanding debt					$ 200,000
Credit Facility | Minimum
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS
Fixed charge coverage ratio						1.5
Credit Facility | Maximum
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS
Total indebtedness to total asset value ratio (as a percent)						60.00%
Credit Facility | Revolver
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS
Maximum borrowing capacity	$ 750,000							$ 500,000
Interest rate, basis spread (as a percent)						1.10%
Facility fee (as a percent)						0.15%
Credit Facility | Unsecured term loan
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS
Debt amount								$ 200,000
Senior notes 4.375% due 2023
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS
Debt amount		$ 50,000		$ 250,000		$ 300,000	300,000
Proceeds from senior notes		$ 50,000		$ 250,000
Interest rate (as a percent)		4.375%		4.375%		4.375%
Effective interest rate (as a percent)		3.495%		4.501%		4.33%
Effective weighted average interest rate (as a percent)						4.33%
Senior notes 4.000% due 2025
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS
Debt amount		$ 50,000	$ 250,000			$ 300,000	300,000
Proceeds from senior notes		$ 50,000	$ 250,000
Interest rate (as a percent)		4.00%	4.00%			4.00%
Effective interest rate (as a percent)		3.811%	4.032%			3.99%
Effective weighted average interest rate (as a percent)						3.994%
Senior Notes 4.375 % Due 2029
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS
Debt amount					$ 350,000	$ 350,000	$ 350,000
Interest rate (as a percent)					4.375%	4.375%
Effective interest rate (as a percent)						4.46%