Notes Receivable and Allowance for Losses - Summary of activity related to allowance for losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	$ 2,137
Ending balance	4,685	$ 2,137
Mezzanine & Other Notes Receivable
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	2,137	2,417
Provisions	2,779	0
Write-offs	(231)	(280)
Ending balance	$ 4,685	$ 2,137