Dispositions - Summary of Dispositions (Details) $ in Thousands																												6 Months Ended
	May 31, 2018 USD ($) ft²	Apr. 19, 2018 USD ($) ft²	Mar. 28, 2018 USD ($) ft²	Mar. 21, 2018 USD ($) ft²	Mar. 20, 2018 USD ($) ft²	Mar. 07, 2018 USD ($) ft²	Feb. 15, 2018 USD ($) ft²	Jan. 19, 2018 USD ($) ft²	Jun. 30, 2017 USD ($) ft²	Jun. 29, 2017 USD ($) ft²	Jun. 16, 2017 USD ($) ft²	Jun. 06, 2017 USD ($) ft²	Jun. 05, 2017 USD ($) ft²	May 31, 2017 USD ($) ft²	May 30, 2017 USD ($) ft²	May 26, 2017 USD ($) ft²	May 25, 2017 USD ($) ft²	May 09, 2017 USD ($) ft²	Apr. 27, 2017 USD ($) ft²	Apr. 04, 2017 USD ($) ft²	Mar. 24, 2017 USD ($) ft²	Mar. 16, 2017 USD ($) ft²	Mar. 15, 2017 USD ($) ft²	Mar. 08, 2017 USD ($) ft²	Mar. 07, 2017 USD ($) ft²	Feb. 21, 2017 USD ($) ft²	Jan. 27, 2017 USD ($) ft²	Jun. 30, 2018 USD ($) ft²	Jun. 30, 2017 USD ($) ft²	Aug. 01, 2018 USD ($) phase unit
Property Dispositions [Line Items]
Aggregate proceeds, net																												$ 187,125	$ 404,996
Gain																												$ 34,519	$ 157,792
Proceeds temporarily restricted related to 1031 Exchanges									$ 93,561
Crown Theater
Property Dispositions [Line Items]
Square footage | ft²								74,200
Consideration								$ 6,900
Aggregate proceeds, net								6,350
Gain								$ 2,952
Cranberry Square
Property Dispositions [Line Items]
Square footage | ft²							195,200
Consideration							$ 23,500
Aggregate proceeds, net							23,163
Gain							$ 10,174
Rite Aid Store (Eckerd) - Crossville, TN
Property Dispositions [Line Items]
Square footage | ft²						13,800
Consideration						$ 1,800
Aggregate proceeds, net						1,768
Gain						$ 157
Home Depot Plaza
Property Dispositions [Line Items]
Square footage | ft²					135,600
Consideration					$ 16,250
Aggregate proceeds, net					15,873
Gain					0
Mortgage payable repaid					$ 10,750
Governor's Marketplace
Property Dispositions [Line Items]
Square footage | ft²				243,100
Consideration				$ 23,500
Aggregate proceeds, net				20,993
Gain				$ 7,429
Stony Creek I & Stony Creek II
Property Dispositions [Line Items]
Square footage | ft²			204,800
Consideration			$ 32,800
Aggregate proceeds, net			32,078
Gain			$ 11,628
CVS Pharmacy - Lawton, OK
Property Dispositions [Line Items]
Square footage | ft²		10,900
Consideration		$ 1,600
Aggregate proceeds, net		1,596
Gain		$ 0
Schaumburg Towers
Property Dispositions [Line Items]
Square footage | ft²	895,400
Consideration	$ 86,600
Aggregate proceeds, net	73,315
Gain	$ 0
2018 dispositions
Property Dispositions [Line Items]
Square footage | ft²																												1,773,000
Consideration																												$ 192,950
Aggregate proceeds, net																												175,136
Gain																												32,340
Condemnation proceeds																												169
Redevelopment portion of Circle East, air rights
Property Dispositions [Line Items]
Aggregate proceeds, net																												11,820
Gain																												$ 2,179
Rite Aid Store (Eckerd), Culver Rd. - Rochester, NY
Property Dispositions [Line Items]
Square footage | ft²																											10,900
Consideration																											$ 500
Aggregate proceeds, net																											332
Gain																											$ 0
Shoppes at Park West
Property Dispositions [Line Items]
Square footage | ft²																										63,900
Consideration																										$ 15,383
Aggregate proceeds, net																										15,261
Gain																										$ 7,569
CVS Pharmacy - Sylacauga, AL
Property Dispositions [Line Items]
Square footage | ft²																									10,100
Consideration																									$ 3,700
Aggregate proceeds, net																									3,348
Gain																									$ 1,651
Proceeds temporarily restricted related to 1031 Exchanges									3,332
Rite Aid Store (Eckerd) - Kill Devil Hills, NC
Property Dispositions [Line Items]
Square footage | ft²																								13,800
Consideration																								$ 4,297
Aggregate proceeds, net																								4,134
Gain																								$ 1,857
Century III Plaza - Home Depot
Property Dispositions [Line Items]
Square footage | ft²																							131,900
Consideration																							$ 17,519
Aggregate proceeds, net																							17,344
Gain																							$ 4,487
Village Shoppes at Gainesville
Property Dispositions [Line Items]
Square footage | ft²																						229,500
Consideration																						$ 41,750
Aggregate proceeds, net																						41,380
Gain																						$ 14,107
Northwood Crossing
Property Dispositions [Line Items]
Square footage | ft²																					160,000
Consideration																					$ 22,850
Aggregate proceeds, net																					22,723
Gain																					$ 10,007
Proceeds temporarily restricted related to 1031 Exchanges									22,719
University Town Center
Property Dispositions [Line Items]
Square footage | ft²																				57,500
Consideration																				$ 14,700
Aggregate proceeds, net																				14,590
Gain																				$ 9,128
Proceeds temporarily restricted related to 1031 Exchanges									14,595
Edgemont Town Center
Property Dispositions [Line Items]
Square footage | ft²																				77,700
Consideration																				$ 19,025
Aggregate proceeds, net																				18,857
Gain																				$ 8,995
Proceeds temporarily restricted related to 1031 Exchanges									18,885
Phenix Crossing
Property Dispositions [Line Items]
Square footage | ft²																				56,600
Consideration																				$ 12,400
Aggregate proceeds, net																				12,296
Gain																				$ 5,699
Proceeds temporarily restricted related to 1031 Exchanges									12,324
Brown's Lane
Property Dispositions [Line Items]
Square footage | ft²																			74,700
Consideration																			$ 10,575
Aggregate proceeds, net																			10,318
Gain																			$ 3,408
Rite Aid Store (Eckerd) - Greer, SC
Property Dispositions [Line Items]
Square footage | ft²																		13,800
Consideration																		$ 3,050
Aggregate proceeds, net																		2,961
Gain																		$ 830
Evans Town Centre
Property Dispositions [Line Items]
Square footage | ft²																		75,700
Consideration																		$ 11,825
Aggregate proceeds, net																		11,419
Gain																		$ 5,226
Red Bug Village
Property Dispositions [Line Items]
Square footage | ft²																	26,200
Consideration																	$ 8,100
Aggregate proceeds, net																	7,767
Gain																	$ 2,184
Wilton Square
Property Dispositions [Line Items]
Square footage | ft²																438,100
Consideration																$ 49,300
Aggregate proceeds, net																48,503
Gain																$ 19,630
Town Square Plaza
Property Dispositions [Line Items]
Square footage | ft²															215,600
Consideration															$ 28,600
Aggregate proceeds, net															26,459
Gain															$ 3,412
Cuyahoga Falls Market Center
Property Dispositions [Line Items]
Square footage | ft²														76,400
Consideration														$ 11,500
Aggregate proceeds, net														11,101
Gain														$ 1,300
Plaza Santa Fe II
Property Dispositions [Line Items]
Square footage | ft²													224,200
Consideration													$ 35,220
Aggregate proceeds, net													33,506
Gain													$ 16,136
Rite Aid Store (Eckerd) - Columbia, SC
Property Dispositions [Line Items]
Square footage | ft²												13,400
Consideration												$ 3,250
Aggregate proceeds, net												3,163
Gain												$ 1,046
Fox Creek Village
Property Dispositions [Line Items]
Square footage | ft²											107,500
Consideration											$ 24,825
Aggregate proceeds, net											24,415
Gain											$ 12,470
Cottage Plaza
Property Dispositions [Line Items]
Square footage | ft²										85,500
Consideration										$ 23,050
Aggregate proceeds, net										22,685
Gain										$ 8,039
Magnolia Square
Property Dispositions [Line Items]
Square footage | ft²										116,000
Consideration										$ 16,000
Aggregate proceeds, net										15,692
Gain										$ 4,866
Cinemark Seven Bridges
Property Dispositions [Line Items]
Square footage | ft²										70,200
Consideration										$ 15,271
Aggregate proceeds, net										14,948
Gain										$ 3,973
Low Country Village I & II
Property Dispositions [Line Items]
Square footage | ft²										139,900
Consideration										$ 22,075
Aggregate proceeds, net										21,639
Gain										$ 10,286
Proceeds temporarily restricted related to 1031 Exchanges									$ 21,706
2017 dispositions
Property Dispositions [Line Items]
Square footage | ft²									2,489,100																				2,489,100
Consideration									$ 414,765																				$ 414,765
Aggregate proceeds, net																													404,841
Gain																													156,306
Condemnation proceeds																													150
Century III Plaza
Property Dispositions [Line Items]
Square footage | ft²																							284,100
Maple Tree Place
Property Dispositions [Line Items]
Aggregate proceeds, net																													5
Gain																													$ 1,486
Subsequent events | One Loudoun Downtown - Land
Property Dispositions [Line Items]
Consideration																														$ 1,800
Number of residential units with development rights | unit																														8
Number of phases | phase																														3
Total number of residential units to be disposed | unit																														30
Total sales price for land and development rights																														$ 6,800