Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net income	$ 28,694	$ (9,499)	$ 17,507	$ 34,232	$ 38,399	$ 83,849	$ 61,793
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization					97,429	100,593	95,345
Amortization of above and below-market leases and lease inducements, net					(6,148)	(5,347)	(4,121)
Amortization of debt premiums, discounts, and financing costs, net					1,706	1,048	1,219
Straight-line rent adjustment, net					(3,464)	(4,262)	(2,202)
Provision for asset impairment					2,359	3,510	27,754
Gain on sale and transfer of investment properties, net					(62,011)	(95,097)	(34,181)
Loss (gain) on extinguishment of debt, net					2,901	(9,103)	(838)
Equity in (earnings) losses and impairment, net, of unconsolidated entities					(957)	31,393	804
Distributions from unconsolidated entities					8,228	8,032	2,443
Realized and unrealized gains on marketable securities, net					0	(244)	(46,563)
Stock-based compensation, net					5,541	4,330	3,355
Provision for indemnification claims					25,500	0	4,500
Changes in operating assets and liabilities:
Accounts and rents receivable, net					(3,510)	(218)	(1,048)
Deferred costs and other assets					(1,624)	1,426	2,051
Accounts payable and accrued expenses					(66)	2,499	5,561
Other liabilities					1,725	2,248	2,280
Net cash provided by operating activities					106,008	124,657	118,152
Cash flows from investing activities:
Purchase of investment properties					(329,493)	(205,462)	(539,242)
Acquired in-place and market lease intangibles, net					(29,602)	(15,369)	(50,207)
Capital expenditures and tenant improvements					(17,754)	(27,233)	(15,910)
Investment in development and re-development projects					(7,103)	(3,796)	(3,630)
Proceeds from the sale and transfer of investment properties, net					346,707	430,514	233,686
Proceeds from the sale of marketable securities, net					0	4,696	171,666
Proceeds from the sale of unconsolidated entity					30,000	0	0
Indemnification payment related to the sale of investment properties					(30,000)	0	0
Contributions to unconsolidated entities					0	(2,782)	(6,875)
Distributions from unconsolidated entities					0	745	1,592
Lease commissions and other leasing costs					(5,621)	(6,029)	(4,356)
Other assets					333	(127)	439
Other liabilities					736	257	3,749
Net cash (used in) provided by investing activities					(41,797)	175,414	(209,088)
Cash flows from financing activities:
Payment of tax withholdings for share-based compensation					(1,397)	(1,567)	(2,192)
Repurchase of common stock under share repurchase plan					(20,384)	0	0
Repurchase of common stock through tender offer					0	(98,447)	0
Distributions to shareholders					(53,250)	(54,194)	(53,358)
Refund received of excess funds associated with 2016 tender offer					0		1,929	$ 0
Proceeds from debt					118,000	179,333	0
Payoffs of debt					(106,041)	(221,358)	(104,032)
Debt prepayment penalties					(1,834)	(3,088)	0
Principal payments of mortgage debt					(2,692)	(1,924)	(1,390)
Payment of loan fees and deposits					(446)	(5,544)	(368)
Payment of finance lease liabilities					(272)	(307)	0
Net cash used in financing activities					(68,316)	(207,096)	(159,411)
Net (decrease) increase in cash, cash equivalents, and restricted cash					(4,105)	92,975	(250,347)
Cash, cash equivalents, and restricted cash at beginning of year		264,853		171,878	264,853	171,878	422,225
Cash, cash equivalents, and restricted cash at end of year	260,748		264,853		260,748	264,853	171,878	422,225
Reconciliation of cash, cash equivalents, and restricted cash to consolidated balance sheets:
Cash and cash equivalents									$ 255,069	$ 260,131	$ 162,747
Restricted cash									5,679	4,722	9,131
Cash, cash equivalents, and restricted cash at end of year	$ 260,748	$ 264,853	$ 264,853	$ 171,878	260,748	171,878	171,878	$ 422,225	260,748	264,853	171,878
Supplemental disclosure of cash flow information:
Cash paid for interest, net of capitalized interest of $101, $0, and $0 for 2019, 2018 and 2017, respectively					21,259	24,096	31,196
Cash paid for income taxes, net of refunds of $498, $1,703, and $918 for 2019, 2018 and 2017, respectively					446	463	625
Distributions payable to shareholders					13,252	13,029	13,441
Recognition of partially deferred gains on property sales									0	12,756	0
Accrued capital expenditures and tenant improvements									1,180	1,679	1,593
Accrued investment in re-development projects					329	67	0
Accrued lease commissions and other leasing costs					136	104	376
Capitalized costs placed in service					29,027	17,786	15,866
Gross issuance of shares for share-based compensation					4,051	4,319	5,916
Purchase of investment properties:
Net investment properties					332,148	206,763	582,660
Accounts and rents receivable, lease intangibles, and deferred costs and other assets					37,103	21,631	69,617
Accounts payable and accrued expenses, lease intangibles, and other liabilities					(10,156)	(7,563)	(21,111)
Assumption of mortgage debt					0	0	(41,717)
Cash outflow for purchase of investment properties, net					359,095	220,831	589,449
Assumption of mortgage principal					0	0	41,000
Capitalized acquisition costs					(2,334)	(430)	(1,911)
Construction escrow accounts					0	975	1,649
Credits and other changes in cash outflow, net					9,003	1,224	3,238
Gross acquisition price of investment properties					365,764	222,600	633,425
Sale and transfer of investment properties:
Net investment properties					286,682	382,241	200,399
Accounts and rents receivable, lease intangibles, and deferred costs and other assets					9,295	14,692	6,658
Accounts payable and accrued expenses, lease intangibles, and other liabilities									$ (9,189)	$ (13,035)	$ (5,047)
Debt extinguished through transfer of properties					0	(44,331)	(3,343)
Debt assumed by buyer through disposition of properties					0	(16,395)	0
Gain on sale and transfer of investment properties, net					62,011	95,097	34,181
(Loss) gain on extinguishment of debt, net					(2,092)	9,157	838
Debt prepayment penalties and defeasance costs					0	3,088	0
Proceeds from sale and transfer of investment properties, net					346,707	430,514	233,686
Assumption of mortgage principal by buyer					0	16,600	0
Surrender of mortgage escrows for transferred properties					0	2,160	6,024
Credits and other changes in cash inflow, net					11,093	16,901	4,356
Gross disposition price of investment properties					$ 357,800	$ 466,175	$ 244,066