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
Mar. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Other assets $ 109,626 $ 122,753 [1] $ 130,923
Carrying Amount [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Cash and cash equivalents 349,945 362,526  
Restricted cash 48,386 46,721  
Loans receivable [2] 7,634 19,454  
Notes receivable, net 424,117 426,858  
Receivable-backed notes payable 413,334 421,118  
Notes payable and other borrowings 125,324 144,114  
Junior subordinated debentures 135,725 135,414  
Redeemable 5% cumulative preferred stock 9,232 13,974  
Carrying Amount [Member] | Preferred Shareholders [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Other assets [2]   5,000  
Fair Value [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Cash and cash equivalents 349,945 362,526  
Restricted cash 48,386 46,721  
Loans receivable [2] 9,183 21,125  
Notes receivable, net 510,000 525,000  
Receivable-backed notes payable 416,300 425,900  
Notes payable and other borrowings 129,559 149,438  
Junior subordinated debentures 130,500 132,000  
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 [2]   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 349,945 362,526  
Restricted cash 48,386 46,721  
Significant Unobservable Inputs (Level 3) [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Loans receivable [2] 9,183 21,125  
Notes receivable, net 510,000 525,000  
Receivable-backed notes payable 416,300 425,900  
Notes payable and other borrowings 129,559 149,438  
Junior subordinated debentures 130,500 132,000  
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 [2]   $ 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 March 31, 2018 and December 31, 2017.