Notes Receivable and Allowance for Losses Narrative (Details) - USD ($)		3 Months Ended	12 Months Ended
	Sep. 12, 2017	Mar. 31, 2018	Dec. 31, 2017
Notes Receivable and Allowance for Losses [Line Items]
Loan reserves		$ 2,137,000	$ 2,137,000
Transfer of notes receivable to third party	$ 24,200,000	200,000
Notes receivable outstanding		95,540,000	93,392,000
Mezzanine & Other Notes Receivable | Impaired Loans
Notes Receivable and Allowance for Losses [Line Items]
Impaired receivables, recorded investment		1,800,000	1,800,000
Impaired receivables, related allowance		1,600,000	1,600,000
Average notes receivable, nonaccrual status		1,800,000	1,900,000
Interest income, impaired loans		0	44,000
Mezzanine & Other Notes Receivable | Non-impaired Loans
Notes Receivable and Allowance for Losses [Line Items]
Loan reserves		500,000	500,000
Notes Receivable
Notes Receivable and Allowance for Losses [Line Items]
Notes receivable outstanding	$ 49,100,000	24,400,000
Variable Interest Entity, Not Primary Beneficiary | Mezzanine & Other Notes Receivable
Notes Receivable and Allowance for Losses [Line Items]
Loans and financing receivable		37,900,000	35,200,000
Interest Rate Below Market Reduction | Variable Interest Entity, Not Primary Beneficiary | Mezzanine & Other Notes Receivable
Notes Receivable and Allowance for Losses [Line Items]
Loans and financing receivable		4,600,000	2,100,000
Receivable with Imputed Interest, discount		300,000	100,000
Other Long-term Liabilities
Notes Receivable and Allowance for Losses [Line Items]
Transfer of notes receivable to third party		$ 24,400,000	$ 24,200,000