New Issued Accounting Pronouncements (Details) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2017 USD ($) center capital_lease administrative_office lease	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)	Oct. 01, 2017 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities	$ 210,204	$ 199,972
Net cash used in financing activities	$ (309,771)	144,641
Acquisition related costs		700	$ 1,400
Number of lessor leases | lease	5,600
Number of properties with ground lease agreements | center	14
Number of administrative office leases | administrative_office	3
Number of capital leases | capital_lease	1
Capital leases assets, number of units | center	2
Obligations under capital leases	$ 21,000		21,000
Capitalized internal costs	7,900	7,800	$ 10,300
Change in restricted deposits and mortgage escrows	20,203	(14,653)
Accounting Standards Update 2016-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities		6,000
Net cash used in financing activities		(6,000)
Accounting Standards Update 2016-18 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in restricted deposits and mortgage escrows	20,000	(15,000)
Accounting Standards Update 2017-07 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net periodic benefit cost, excluding the service cost component	$ 300	$ 400
Scenario, Forecast [Member] | Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption				$ 500