Segment Reporting - Segment Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information, Additional Information
Assets	$ 4,587,470	$ 4,698,923
Operating Segments | Net Lease
Segment Reporting Information, Additional Information
Assets	3,980,445	3,905,402
Operating Segments | Self-Storage
Segment Reporting Information, Additional Information
Assets	241,438	252,195
Operating Segments | All Other
Segment Reporting Information, Additional Information
Assets	277,702	266,231
Corporate
Segment Reporting Information, Additional Information
Assets	$ 87,885	$ 275,095