Real Estate Properties - Pro Forma (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) $ / shares
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Rental income	$ 189,446
Net income	$ 9,453
Net income per common share (in dollars per share) | $ / shares	$ 0.20
Acquisition-related costs
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Decrease in revenues	$ 40,605
Decrease in net income	$ 13,312