New Issued Accounting Pronouncements (Details) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2017 USD ($) center capital_lease administrative_office lease	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities	$ 132,938	$ 123,726
Net cash used in financing activities	$ (181,748)	(81,507)
Acquisition related costs		200	$ 1,400
Number of lessor leases | lease	5,700
Number of properties with ground lease agreements | center	15
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	$ 5,400	5,100	$ 10,300
Accounting Standards Update 2016-09, Statutory Tax Withholding Component [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