Notes Receivable and Allowance for Losses - Schedule of notes receivable (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total notes receivable	$ 125,911	$ 94,444
Allowance for losses on non-impaired loans	6,660	5,979
Allowance for losses on receivables specifically evaluated for impairment	770	786
Total loan reserves	7,430	6,765
Net carrying value	118,481	87,679
Current portion, net	7,873	5,107
Long-term portion, net	110,608	82,572
Senior
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total notes receivable	61,482	40,388
Subordinated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total notes receivable	9,336	6,197
Unsecured
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total notes receivable	55,093	47,859
Forgivable Notes Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total notes receivable	51,475	44,333
Allowance for losses on non-impaired loans	5,013	4,615
Allowance for losses on receivables specifically evaluated for impairment	0	0
Total loan reserves	5,013	4,615	$ 3,661
Net carrying value	46,462	39,718
Current portion, net	333	143
Long-term portion, net	46,129	39,575
Forgivable Notes Receivable | Senior
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total notes receivable	0	0
Forgivable Notes Receivable | Subordinated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total notes receivable	0	0
Forgivable Notes Receivable | Unsecured
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total notes receivable	51,475	44,333
Mezzanine & Other Notes Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total notes receivable	74,436	50,111
Allowance for losses on non-impaired loans	1,647	1,364
Allowance for losses on receivables specifically evaluated for impairment	770	786
Total loan reserves	2,417	2,150	$ 2,326
Net carrying value	72,019	47,961
Current portion, net	7,540	4,964
Long-term portion, net	64,479	42,997
Mezzanine & Other Notes Receivable | Senior
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total notes receivable	61,482	40,388
Mezzanine & Other Notes Receivable | Subordinated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total notes receivable	9,336	6,197
Mezzanine & Other Notes Receivable | Unsecured
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total notes receivable	$ 3,618	$ 3,526