Schedule IV - Mortgage Loans on Real Estate Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Mortgage Loans on Real Estate [Roll Forward]
Balance as of the beginning of the year	$ 12,737	$ 0	$ 0
Additions:
New mortgage loans	0	12,737	0
Deductions:
Mortgage loan included in the consideration for the acquisition of a building	0	0	0
Collection of mortgage loans	(9,964)	0	0
Balance as of the end of the year	$ 2,773	$ 12,737	$ 0