Notes Receivable and Allowance for Losses - Past due balances of mezzanine and other notes receivable (Details) - Mezzanine & Other Notes Receivable - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	$ 0	$ 0
Current	74,436	50,111
Total Mezzanine and Other Notes Receivables	74,436	50,111
Senior
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	0	0
Current	61,482	40,388
Total Mezzanine and Other Notes Receivables	61,482	40,388
Subordinated
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	0	0
Current	9,336	6,197
Total Mezzanine and Other Notes Receivables	9,336	6,197
Unsecured
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	0	0
Current	3,618	3,526
Total Mezzanine and Other Notes Receivables	3,618	3,526
Financing Receivables, 30 to 89 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	0	0
Financing Receivables, 30 to 89 Days Past Due | Senior
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	0	0
Financing Receivables, 30 to 89 Days Past Due | Subordinated
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	0	0
Financing Receivables, 30 to 89 Days Past Due | Unsecured
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	0	0
Financing Receivables, Equal to Greater than 90 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	0	0
Financing Receivables, Equal to Greater than 90 Days Past Due | Senior
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	0	0
Financing Receivables, Equal to Greater than 90 Days Past Due | Subordinated
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	0	0
Financing Receivables, Equal to Greater than 90 Days Past Due | Unsecured
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	$ 0	$ 0