Notes Receivable and Allowance for Losses Past Due Balances Of Mezzanine And Other Notes Receivable (Details) - Mezzanine & Other Notes Receivable - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Notes Receivable and Allowance for Losses [Line Items]
Total Past Due	$ 0	$ 0
Current	117,813	95,529
Total Notes Receivable	117,813	95,529
Senior
Notes Receivable and Allowance for Losses [Line Items]
Total Past Due	0	0
Current	89,568	73,700
Total Notes Receivable	89,568	73,700
Subordinated
Notes Receivable and Allowance for Losses [Line Items]
Total Past Due	0	0
Current	25,728	18,647
Total Notes Receivable	25,728	18,647
Unsecured
Notes Receivable and Allowance for Losses [Line Items]
Total Past Due	0	0
Current	2,517	3,182
Total Notes Receivable	2,517	3,182
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