Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 205,745	$ 197,337
Restricted cash	53,653	46,012
Notes receivable, net	429,647	426,858
Lines-of-credit, notes payable, and receivable-backed notes payable	576,745	521,312
Junior subordinated debentures	70,908	70,384
Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	205,745	197,337
Restricted cash	53,653	46,012
Notes receivable, net	520,000	525,000
Lines-of-credit, notes payable, and receivable-backed notes payable	575,900	529,400
Junior subordinated debentures	$ 91,000	$ 88,500