Summary of Significant Accounting Policies - Additional Information (Detail)		3 Months Ended		9 Months Ended
	Jun. 11, 2015 JointVenture	Sep. 30, 2018 USD ($) Property State	Sep. 30, 2017 USD ($) shares	Sep. 30, 2018 USD ($) Property JointVenture State Segment	Sep. 30, 2017 USD ($) shares	Aug. 29, 2018 shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 shares
Summary Of Significant Accounting Policies [Line Items]
Number of reportable segments | Segment				1
Impairment loss on real estate assets		$ 0	$ 0	$ 0	$ 0
Impairment loss		0	0	0	0
Restricted cash		$ 0	$ 202,513,000	$ 0	202,513,000		$ 175,665,000
Prepaid rental income							$ 2,700,000
Revenue performance obligation satisfied over time method used description				Management determined that property and asset management and construction and development management services each represent a series of stand-ready performance obligations satisfied over time with each day of service being a distinct performance obligation.
Number of wholly owned properties acquired | Property		211		211
Number of joint venture properties acquired | JointVenture				26
Number of states in properties located | State		48		48
Decrease to net cash provided by operating activities				$ (14,296,000)	(46,234,000)
Decrease to net cash used in investing activities				$ 47,276,000	(50,884,000)
ASU 2016-15 [Member]
Summary Of Significant Accounting Policies [Line Items]
Decrease to net cash provided by operating activities					10,714,000
Decrease to net cash used in investing activities					$ 10,714,000
ASU 2014-09 [Member] | Santa Monica, CA [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of interests sold		49.90%		49.90%
ASU 2014-09 [Member] | West Hartford, CT [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of interests sold		50.00%		50.00%
Class C Common Shares [Member]
Summary Of Significant Accounting Policies [Line Items]
Common shares, outstanding | shares			5,952,000		5,952,000	0	3,151,131	5,755,000
Interest Rate Cap [Member]
Summary Of Significant Accounting Policies [Line Items]
Interest rate caps purchased		$ 5,000,000		$ 5,000,000
Derivative, term of contract				4 years
Notional amount		1,261,000,000		$ 1,261,000,000
Derivative strike rate				3.50%
Derivative losses		$ 16,000	$ 100,000	$ 23,000	$ 700,000
Master Lease [Member]
Summary Of Significant Accounting Policies [Line Items]
Right to recapture property space		50.00%		50.00%
Sears Holdings Corporation [Member]
Summary Of Significant Accounting Policies [Line Items]
Right to recapture property space		100.00%		100.00%
Number of joint venture properties acquired | JointVenture	3
Sears Holdings Corporation [Member] | Master Lease [Member]
Summary Of Significant Accounting Policies [Line Items]
Right to recapture property space		100.00%		100.00%
Management and Other Fee Income [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of revenue earned from unconsolidated joint ventures				100.00%
Restricted Cash Reserves [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash							$ 151,300,000
Basic Property Carrying Costs [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash							$ 21,700,000
Operating Partnership [Member] | ESL [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of operating partnership interest held by parent		63.90%		63.90%