Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Cash flows from operating activities:
Net income	$ (7,347)	$ 21,170	$ 15,010	$ 44,378
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization			83,928	86,149
Provision for impairment of investment properties	0	0	346	0	$ 12,298
Gain on sales of investment properties	0	(8,454)	0	(16,903)
Amortization of loan fees and debt premium and discount, net			1,912	1,597
Amortization of stock-based compensation			4,454	3,823
Payment of leasing fees and inducements			(4,356)	(5,120)
Reserve for bad debt, net			13,977	589
Changes in accounts receivable			(31,647)	1,332
Changes in right-of-use lease assets			928	961
Changes in accounts payable and accrued expenses, net			(21,899)	(16,999)
Changes in lease liabilities			33	(309)
Changes in other operating assets and liabilities, net			2,696	4,234
Other, net			(957)	(4,546)
Net cash provided by operating activities			64,425	99,186
Cash flows from investing activities:
Purchase of investment properties			(54,970)	(26,576)
Capital expenditures and tenant improvements			(30,778)	(39,934)
Proceeds from sales of investment properties			11,369	41,886
Investment in developments in progress			(32,499)	(7,784)
Net cash used in investing activities			(106,878)	(32,408)
Cash flows from financing activities:
Principal payments on mortgages payable			(1,242)	(1,530)
Proceeds from unsecured notes payable			0	100,000
Proceeds from unsecured revolving line of credit			937,704	143,000
Repayments of unsecured revolving line of credit			(820,704)	(223,000)
Payment of loan fees and deposits			(151)	(754)
Distributions paid			(70,851)	(70,758)
Other, net			900	(10)
Net cash provided by (used in) financing activities			45,656	(53,052)
Net increase in cash, cash equivalents and restricted cash			3,203	13,726
Cash, cash equivalents and restricted cash, at beginning of period			14,447	19,601	19,601
Cash, cash equivalents and restricted cash, at end of period	17,650	33,327	17,650	33,327	14,447
Supplemental cash flow disclosure, including non-cash activities:
Cash paid for interest, net of interest capitalized			34,234	33,276
Cash paid for amounts included in the measurement of operating lease liabilities			2,505	3,052
Cash received for accounts receivable previously written off			54	112
Distributions payable	0	35,388	0	35,388	35,387
Accrued capital expenditures and tenant improvements			8,938	7,403
Accrued leasing fees and inducements			1,127	673
Accrued redevelopment costs			2,531	281
Amounts reclassified to developments in progress			305	13,570
Change in noncontrolling interest due to termination of joint ventures			2,217	0
Lease liabilities arising from obtaining right-of-use lease assets			383	103,519
Straight-line ground rent liabilities reclassified to right-of-use lease asset			0	31,030
Straight-line office rent liability reclassified to right-of-use lease asset			0	507
Acquired ground lease intangible liability reclassified to right-of-use lease asset			0	11,898
Purchase of investment properties (after credits at closing):
Net investment properties			(58,760)	(25,438)
Right-of-use lease assets			5,999	0
Accounts receivable, acquired lease intangibles and other assets			(1,801)	(1,525)
Lease liabilities			(5,942)	0
Accounts payable, acquired lease intangibles and other liabilities			5,534	387
Purchase of investment properties (after credits at closing)			(54,970)	(26,576)
Proceeds from sales of investment properties:
Net investment properties			11,307	29,318
Right-of-use lease assets			0	8,242
Accounts receivable, acquired lease intangibles and other assets			167	1,591
Lease liabilities			0	(11,326)
Accounts payable, acquired lease intangibles and other liabilities			(105)	(2,842)
Gain on sales of investment properties	0	8,454	0	16,903
Proceeds from sales of investment properties			11,369	41,886
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents, at beginning of period			9,989	14,722	14,722
Restricted cash, at beginning of period (included within “Other assets, net”)			4,458	4,879	4,879
Cash, cash equivalents and restricted cash, at beginning of period			14,447	19,601	19,601
Cash and cash equivalents, at end of period	12,563	28,456	12,563	28,456	9,989
Restricted cash, at end of period (included within “Other assets, net”)	5,087	4,871	5,087	4,871	4,458
Cash, cash equivalents and restricted cash, at end of period	$ 17,650	$ 33,327	$ 17,650	$ 33,327	$ 14,447