Real Estate Assets (Details) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2018 USD ($) a	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($) a parcel	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) a	Sep. 30, 2017 USD ($)
Acquisitions [Abstract]
Undeveloped land suitable for future development (in acres) | a	350				350
Dispositions [Abstract]
Gains on disposition of property	$ 3			$ 19,849	$ 16,975	$ 25,181
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	$ 2,100	$ 34,000
Gains on disposition of property		$ 17,000