Real Estate Properties - Pro Forma (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Decrease in revenues	$ (176,032)	$ (108,085)	$ (350,809)	$ (216,802)
Rental income				375,258
Net income				$ 33,266
Net income per common share (in dollars per share)				$ 0.69
Acquisition-related costs
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Decrease in revenues				$ 80,025
Decrease in net income				$ 26,273