Summary of Significant Accounting Policies and Procedures and Recent Accounting Pronouncements - Provision For Impairment (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) property	Dec. 31, 2017 USD ($) property	Dec. 31, 2016 USD ($) property
Provision for Impairment
Number of properties	5,797
Total provisions for impairment | $	$ 26,300,000	$ 14,800,000	$ 20,700,000
Number of impaired properties held-for-sale	6	1	1
Number of impaired properties held-for-investment	3	3
Number of impaired properties sold	35	22	38
Impairment on existing goodwill | $	$ 0	$ 0	$ 0
Held for sale
Provision for Impairment
Number of properties	17