Schedule III - Carrying Cost and Accumulated Depreciation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Carrying cost:
Gross amount at beginning	$ 7,394,951	$ 7,000,099
Tenant capital improvements	102,396	164,742	$ 153,615
Growth capital improvements	84,700
Acquisitions	220,674	293,562
Other	170	26,736
Total additions	407,940	485,040
Cost of real estate sold or disposed	414,976	90,188
Total deductions	414,976	90,188
Balance at end	7,387,915	7,394,951	7,000,099
Accumulated depreciation:
Gross amount of accumulated depreciation at beginning	5,022,929	4,739,126
Depreciation	202,877	291,398
Other		1,767
Total additions	202,877	293,165
Amount of accumulated depreciation for assets sold or disposed	20,411	9,362
Total deductions	20,411	9,362
Balance at end	$ 5,205,395	$ 5,022,929	$ 4,739,126