Notes Receivable and Allowance for Losses - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Notes Receivable and Allowance for Losses [Line Items]
Loan reserves	$ 4,685,000		$ 4,685,000
Mezzanine & Other Notes Receivable
Notes Receivable and Allowance for Losses [Line Items]
Impaired financing receivable, unpaid principal balance	51,800,000		51,800,000
Mezzanine & Other Notes Receivable | Impaired Loans
Notes Receivable and Allowance for Losses [Line Items]
Impaired receivables, recorded investment	52,400,000		52,100,000
Impaired receivables, related allowance	4,400,000		4,400,000
Average notes receivable, nonaccrual status	27,100,000	$ 1,800,000
Interest income, impaired loans	0	$ 0
Mezzanine & Other Notes Receivable | Non-impaired Loans
Notes Receivable and Allowance for Losses [Line Items]
Loan reserves	300,000		300,000
Variable Interest Entity, Not Primary Beneficiary | Mezzanine & Other Notes Receivable
Notes Receivable and Allowance for Losses [Line Items]
Loans and financing receivable	111,900,000		114,300,000
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	13,800,000		12,900,000
Receivable with Imputed Interest, discount	$ 1,400,000		$ 1,500,000