Schedule III - Carrying Cost and Accumulated Depreciation (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($)
Carrying cost:
Gross amount at beginning	$ 6,093,541
Tenant capital improvements	156,972
Acquisitions	15,848
Total additions	172,820
Cost of real estate sold or disposed	10,113
Total deductions	10,113
Balance at end	6,256,248
Accumulated depreciation:
Gross amount of accumulated depreciation at beginning	3,720,890
Depreciation	343,971
Total additions	343,971
Other	10,113
Total deductions	10,113
Balance at end	$ 4,054,748