Variable Interest Entities (Information Related To The Assets And Liabilities Of The VIEs) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Variable Interest Entity [Line Items]
Restricted cash	$ 47,524	$ 46,012	[1]
Securitized notes receivable, net	424,117	426,858	[1]	$ 425,800
Receivable backed notes payable - non-recourse	327,024	336,421	[1]
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Restricted cash	21,240	19,488
Securitized notes receivable, net	294,357	279,188
Receivable backed notes payable - non-recourse	$ 327,024	$ 336,421

[1] * See Note 2 for summary of adjustments.