Investment in Unconsolidated Joint Ventures - Summary of Financial Position and Operations (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
SUMMARY OF FINANCIAL POSITION:
Total Assets	$ 7,106,182		$ 7,107,398
Total Equity	4,450,955		4,467,134
SUMMARY OF OPERATIONS:
Total Revenues	189,550	$ 193,898
Net Income (Loss)	29,110	$ 174,943
Equity Method Investment, Nonconsolidated Investee or Group of Investees
SUMMARY OF FINANCIAL POSITION:
Total Assets	587,355		590,853
Total Debt	288,335		230,305
Total Equity	185,100		244,186
Company’s Investment	81,042		107,192
SUMMARY OF OPERATIONS:
Total Revenues	15,515		19,455
Net Income (Loss)	3,993		6,372
Company's Share of Income (Loss)	1,903		3,425
DC Charlotte Plaza LLLP | Equity Method Investment, Nonconsolidated Investee or Group of Investees
SUMMARY OF FINANCIAL POSITION:
Total Assets	172,479		173,704
Total Debt	0		0
Total Equity	90,542		90,648
Company’s Investment	47,853		47,941
SUMMARY OF OPERATIONS:
Total Revenues	5,059		5,276
Net Income (Loss)	1,795		1,789
Company's Share of Income (Loss)	836		750
Austin 300 Colorado Project, LP | Equity Method Investment, Nonconsolidated Investee or Group of Investees
SUMMARY OF FINANCIAL POSITION:
Total Assets	166,909		165,586
Total Debt	88,159		86,848
Total Equity	68,760		68,567
Company’s Investment	38,855		38,488
SUMMARY OF OPERATIONS:
Total Revenues	1,672		98
Net Income (Loss)	193		44
Company's Share of Income (Loss)	84		22
AMCO 120 WT Holdings, LLC | Equity Method Investment, Nonconsolidated Investee or Group of Investees
SUMMARY OF FINANCIAL POSITION:
Total Assets	85,688		85,449
Total Debt	0		0
Total Equity	84,176		84,311
Company’s Investment	15,716		15,735
SUMMARY OF OPERATIONS:
Total Revenues	1,607		138
Net Income (Loss)	(135)		(509)
Company's Share of Income (Loss)	(21)		(141)
HICO Victory Center LP | Equity Method Investment, Nonconsolidated Investee or Group of Investees
SUMMARY OF FINANCIAL POSITION:
Total Assets	15,923		16,544
Total Debt	0		0
Total Equity	15,813		15,709
Company’s Investment	10,638		10,595
SUMMARY OF OPERATIONS:
Total Revenues	83		126
Net Income (Loss)	83		126
Company's Share of Income (Loss)	42		63
Carolina Square Holdings LP | Equity Method Investment, Nonconsolidated Investee or Group of Investees
SUMMARY OF FINANCIAL POSITION:
Total Assets	117,694		118,616
Total Debt	134,284		77,034
Total Equity	(35,227)		21,888
Company’s Investment	(12,988)		12,430
SUMMARY OF OPERATIONS:
Total Revenues	3,977		3,706
Net Income (Loss)	1,088		530
Company's Share of Income (Loss)	520		254
Charlotte Gateway Village, LLC | Equity Method Investment, Nonconsolidated Investee or Group of Investees
SUMMARY OF OPERATIONS:
Total Revenues	0		6,572
Net Income (Loss)	(4)		3,296
Company's Share of Income (Loss)	(2)		1,647
Crawford Long - CPI, LLC | Equity Method Investment, Nonconsolidated Investee or Group of Investees
SUMMARY OF FINANCIAL POSITION:
Total Assets	27,349		29,641
Total Debt	65,892		66,423
Total Equity	(40,280)		(38,253)
Company’s Investment	(19,323)		(18,289)
SUMMARY OF OPERATIONS:
Total Revenues	3,117		3,343
Net Income (Loss)	973		1,035
Company's Share of Income (Loss)	444		497
Other | Equity Method Investment, Nonconsolidated Investee or Group of Investees
SUMMARY OF FINANCIAL POSITION:
Total Assets	1,313		1,313
Total Debt	0		0
Total Equity	1,316		1,316
Company’s Investment	291		292
SUMMARY OF OPERATIONS:
Total Revenues	0		196
Net Income (Loss)	0		61
Company's Share of Income (Loss)	$ 0		$ 333