Acquisitions, Dispositions and Mortgage Repayments - Additional information (Details) $ in Millions	1 Months Ended	12 Months Ended
	Oct. 31, 2017 USD ($) property building Purchase_options	Dec. 31, 2017 USD ($) renewal_option	Dec. 31, 2016 USD ($)
Acquisitions and Dispositions and Mortgage Repayments [Abstract]
Number of properties exercising purchase option | property	7
Number of single-tenant net leased buildings exercising purchase option | building	5
Number of multi-tenant buildings exercisng purchase option | building	2
Number of purchase options	1	4
Stated purchase price | $	$ 45.5	$ 122.7	$ 94.7
Aggregate net book value of potential dispositions | $		$ 23.9