Real Estate Assets (Details) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2018 USD ($) a	Mar. 31, 2018 USD ($) a parcel	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) a	Jun. 30, 2017 USD ($)
Acquisitions [Abstract]
Undeveloped land suitable for future development (in acres) | a	400			400
Dispositions [Abstract]
Gains on disposition of property	$ 16,972		$ 0	$ 16,972	$ 5,332
Nashville TN Land Acquisition [Member]
Acquisitions [Abstract]
Number of development parcels acquired (in parcels) | parcel		2
Undeveloped land suitable for future development (in acres) | a		9
Purchase price of acquisition		$ 50,600
2018 Dispositions [Member]
Dispositions [Abstract]
Purchase price of real estate	34,000
Gains on disposition of property	$ 17,000