Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net income	$ 32,397	$ 77,640	$ 251,491
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	194,573	175,977	203,866
Provision for impairment of investment properties	12,298	2,079	67,003
Gain on sales of investment properties	(18,872)	(37,211)	(337,975)
Amortization of loan fees and debt premium and discount, net	2,863	3,416	7,655
Amortization of stock-based compensation	7,559	6,992	6,059
Premium paid in connection with defeasance of mortgages payable	0	0	59,968
Debt prepayment fees	8,151	5,791	8,498
Payment of leasing fees and inducements	(10,436)	(8,775)	(15,981)
Changes in accounts receivable, net	4,830	(8,395)	962
Changes in right-of-use lease assets	1,923	0	0
Changes in accounts payable and accrued expenses, net	129	(6,398)	579
Changes in lease liabilities	(630)	0	0
Changes in other operating assets and liabilities, net	2,935	(672)	(1,770)
Other, net	(6,229)	(6,281)	(2,839)
Net cash provided by operating activities	231,491	204,163	247,516
Cash flows from investing activities:
Purchase of investment properties	(29,891)	(25,450)	(200,755)
Capital expenditures and tenant improvements	(75,597)	(72,936)	(73,750)
Proceeds from sales of investment properties	44,656	197,887	896,456
Investment in developments in progress	(29,470)	(12,226)	(13,649)
Net cash (used in) provided by investing activities	(90,302)	87,275	608,302
Cash flows from financing activities:
Principal payments on mortgages payable	(110,546)	(81,788)	(106,722)
Proceeds from unsecured notes payable	100,000	0	0
Proceeds from unsecured term loans	270,000	0	200,000
Repayments of unsecured term loans	0	(100,000)	(100,000)
Proceeds from unsecured revolving line of credit	263,000	482,000	943,000
Repayments of unsecured revolving line of credit	(518,000)	(425,000)	(813,000)
Payment of loan fees and deposits	(2,519)	(5,954)	(10)
Debt prepayment fees	(8,151)	(5,791)	(8,498)
Purchase of U.S. Treasury securities in connection with defeasance of mortgages payable	0	0	(439,403)
Redemption of preferred stock	0	0	(135,000)
Distributions paid	(141,528)	(145,333)	(163,684)
Shares repurchased through common stock repurchase program	0	(74,952)	(227,102)
Other, net	1,401	(1,354)	(1,413)
Net cash used in financing activities	(146,343)	(358,172)	(851,832)
Net (decrease) increase in cash, cash equivalents and restricted cash	(5,154)	(66,734)	3,986
Cash, cash equivalents and restricted cash, at beginning of year	19,601	86,335	82,349
Cash, cash equivalents and restricted cash, at end of year	14,447	19,601	86,335
Supplemental cash flow disclosure, including non-cash activities:
Cash paid for interest, net of interest capitalized	74,154	70,564	78,327
Cash paid for amounts included in the measurement of operating lease liabilities	6,011	0	0
Distributions payable	35,387	35,387	36,311
Accrued capital expenditures and tenant improvements	7,477	16,007	7,902
Accrued leasing fees and inducements	1,903	530	547
Accrued redevelopment costs	2,185	41	750
Amounts reclassified into developments in progress	34,746	0	0
Developments in progress placed in service	1,377	11,997	0
Lease liabilities arising from obtaining right-of-use lease assets	103,840	0	0
Straight-line ground rent liabilities reclassified to right-of-use lease asset	31,030	0	0
Straight-line office rent liability reclassified to right-of-use lease asset	507	0	0
Acquired ground lease intangible liability reclassified to right-of-use lease asset	11,898	0	0
U.S. Treasury securities transferred in connection with defeasance of mortgages payable	0	0	439,403
Defeasance of mortgages payable	0	0	379,435
Purchase of investment properties (after credits at closing):
Net investment properties	(28,486)	(25,450)	(198,984)
Accounts receivable, acquired lease intangibles and other assets	(1,792)	0	(15,451)
Accounts payable, acquired lease intangibles and other liabilities	387	0	11,156
Gain on exchange of investment property	0	0	2,524
Purchase of investment properties (after credits at closing)	(29,891)	(25,450)	(200,755)
Proceeds from sales of investment properties:
Net investment properties	30,119	156,248	556,129
Right-of-use lease assets	8,242	0	0
Accounts receivable, acquired lease intangibles and other assets	1,591	11,279	17,678
Lease liabilities	(11,326)	0	0
Accounts payable, acquired lease intangibles and other liabilities	(2,842)	(6,851)	(11,316)
Deferred gain	0	0	(1,486)
Gain on sales of investment properties, excluding gain on exchange of investment property	18,872	37,211	335,451
Proceeds from sales of investment properties	44,656	197,887	896,456
Reconciliation of cash, cash equivalents and restricted cash, at end of year:
Cash and cash equivalents	9,989	14,722	25,185
Restricted cash (included within “Other assets, net”)	4,458	4,879	61,150
Cash, cash equivalents and restricted cash, at end of year	$ 14,447	$ 19,601	$ 86,335