Segment Reporting - Segment Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Segment Reporting Information, Additional Information
Assets	$ 4,593,124	$ 4,587,470
Operating Segments | Net Lease
Segment Reporting Information, Additional Information
Assets	4,017,437	3,980,445
Operating Segments | Self Storage
Segment Reporting Information, Additional Information
Assets	240,648	241,438
All Other
Segment Reporting Information, Additional Information
Assets	264,629	277,702
Corporate
Segment Reporting Information, Additional Information
Assets	$ 70,410	$ 87,885