Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurement (Financial Disclosures About Fair Value Of Financial Instruments) (Details)

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Fair Value Measurement (Financial Disclosures About Fair Value Of Financial Instruments) (Details) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Other assets $ 115,437 $ 122,753 [1] $ 130,923
Carrying Amount [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Cash and cash equivalents 380,447 362,526  
Restricted cash 54,471 46,721  
Loans receivable [2] 6,413 19,454  
Notes receivable, net 429,647 426,858  
Receivable-backed notes payable 427,094 421,118  
Notes payable and other borrowings 219,615 144,114  
Junior subordinated debentures 135,974 135,414  
Redeemable 5% cumulative preferred stock 9,310 13,974  
Carrying Amount [Member] | Preferred Shareholders [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Other assets [3]   5,000  
Fair Value [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Cash and cash equivalents 380,447 362,526  
Restricted cash 54,471 46,721  
Loans receivable [2] 7,576 21,125  
Notes receivable, net 520,000 525,000  
Receivable-backed notes payable 424,200 425,900  
Notes payable and other borrowings 223,296 149,438  
Junior subordinated debentures 138,000 132,000  
Redeemable 5% cumulative preferred stock 9,053 13,977  
Fair Value [Member] | Preferred Shareholders [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Other assets [3]   5,000  
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Cash and cash equivalents 380,447 362,526  
Restricted cash 54,471 46,721  
Significant Unobservable Inputs (Level 3) [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Loans receivable [2] 7,576 21,125  
Notes receivable, net 520,000 525,000  
Receivable-backed notes payable 424,200 425,900  
Notes payable and other borrowings 223,296 149,438  
Junior subordinated debentures 138,000 132,000  
Redeemable 5% cumulative preferred stock $ 9,053 13,977  
Significant Unobservable Inputs (Level 3) [Member] | Preferred Shareholders [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Other assets [3]   $ 5,000  
[1] See Note 1 for a summary of adjustments.
[2] Included in other assets in the Company's condensed consolidated statements of financial condition as of June 30, 2018 and December 31, 2017.
[3] Included in other assets in the Company's condensed consolidated statements of financial condition as of December 31, 2017.