Notes Receivable and Allowance for Losses - Past Due Balances Of Mezzanine And Other Notes Receivable (Details) - Mezzanine & Other Notes Receivable - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Notes Receivable and Allowance for Losses [Line Items]
Total Past Due	$ 0	$ 0
Current	122,909	124,884
Total Notes Receivable	122,909	124,884
Senior
Notes Receivable and Allowance for Losses [Line Items]
Total Past Due	0	0
Current	91,115	94,349
Total Notes Receivable	91,115	94,349
Subordinated
Notes Receivable and Allowance for Losses [Line Items]
Total Past Due	0	0
Current	29,270	28,100
Total Notes Receivable	29,270	28,100
Unsecured
Notes Receivable and Allowance for Losses [Line Items]
Total Past Due	0	0
Current	2,524	2,435
Total Notes Receivable	2,524	2,435
Financing Receivables, 30 to 89 Days Past Due
Notes Receivable and Allowance for Losses [Line Items]
Total Past Due	0	0
Financing Receivables, 30 to 89 Days Past Due | Senior
Notes Receivable and Allowance for Losses [Line Items]
Total Past Due	0	0
Financing Receivables, 30 to 89 Days Past Due | Subordinated
Notes Receivable and Allowance for Losses [Line Items]
Total Past Due	0	0
Financing Receivables, 30 to 89 Days Past Due | Unsecured
Notes Receivable and Allowance for Losses [Line Items]
Total Past Due	0	0
Financing Receivables, Equal to Greater than 90 Days Past Due
Notes Receivable and Allowance for Losses [Line Items]
Total Past Due	0	0
Financing Receivables, Equal to Greater than 90 Days Past Due | Senior
Notes Receivable and Allowance for Losses [Line Items]
Total Past Due	0	0
Financing Receivables, Equal to Greater than 90 Days Past Due | Subordinated
Notes Receivable and Allowance for Losses [Line Items]
Total Past Due	0	0
Financing Receivables, Equal to Greater than 90 Days Past Due | Unsecured
Notes Receivable and Allowance for Losses [Line Items]
Total Past Due	$ 0	$ 0