Property Acquisitions and Dispositions - Acquisitions of Operating Stores (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018 USD ($) store shares	Sep. 30, 2018 USD ($) store shares	Jun. 30, 2018 USD ($) store shares	Mar. 31, 2018 USD ($) store shares	Dec. 31, 2017 USD ($) store shares	Sep. 30, 2017 USD ($) store shares	Jun. 30, 2017 USD ($) store shares	Mar. 31, 2017 USD ($) store shares	Dec. 31, 2018 USD ($) store shares	Dec. 31, 2017 USD ($) store shares
Real Estate [Abstract]
Number of stores | store	6	6	17	5	37	4	3	2	34	46
Total	$ 74,852	$ 74,694	$ 237,284	$ 70,787	$ 535,299	$ 31,966	$ 34,641	$ 25,556	$ 457,617	$ 627,462
Cash Paid	74,868	71,989	148,650	70,171	502,845	29,919	16,608	25,541	365,678	574,913
Loan Assumed	0	0	87,500	0	14,592	0	9,463	0	87,500	24,055
Non- controlling interests	0	0	0	0	(1,812)	0	1,827	0	0	15
Investments in Real Estate Ventures	0	0	(1,024)	489	12,957	0	0	0	(535)	12,957
Net Liabilities/ (Assets) Assumed	(16)	2,705	281	127	1,099	47	(67)	15	3,097	1,094
Value of OP Units Issued	$ 0	$ 0	$ 1,877	$ 0	$ 5,618	$ 2,000	$ 6,810	$ 0	$ 1,877	$ 14,428
Number of units issued (in shares) | shares	0	0	21,768	0	64,708	25,520	272,400	0	21,768	362,628
Real estate assets	$ 74,852	$ 74,694	$ 237,284	$ 70,787	$ 535,299	$ 31,966	$ 34,641	$ 25,556	$ 457,617	$ 627,462
Number of stores acquired, previously held noncontrolling interest | store									15
Number of stores acquired, previously held equity interest | store										7