Quarterly report pursuant to Section 13 or 15(d)

Fair Value of Assets and Liabilities (Schedule of Fair Value of Assets and Liabilities Measured on a Nonrecurring Basis) (Details)

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Fair Value of Assets and Liabilities (Schedule of Fair Value of Assets and Liabilities Measured on a Nonrecurring Basis) (Details) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Liabilities    
Contingent consideration liabilities $ 1,766 $ 2,104
Carrying Value | Fair Value, Measurements, Nonrecurring    
Assets    
Cash and cash equivalents 204,847 172,103
Notes receivable, net 5,893 47,369
Other receivables, net 129,182 60,707
Total assets 387,455 331,544
Liabilities    
Accrued compensation 27,418 33,343
Commissions and fees payable 105,194 67,221
Accounts payable and accrued liabilities 52,403 38,374
Accrued interest 191 232
Notes payable, net 136,171 96,849
Total liabilities 321,377 236,019
Fair Value | Level 2    
Liabilities    
Notes payable, net 140,490 99,129
Fair Value | Fair Value, Measurements, Nonrecurring    
Assets    
Cash and cash equivalents 204,847 172,103
Notes receivable, net 5,893 47,369
Other receivables, net 129,182 60,707
Total assets 387,455 331,544
Liabilities    
Accrued compensation 27,418 33,343
Commissions and fees payable 105,194 67,221
Accounts payable and accrued liabilities 52,403 38,374
Accrued interest 191 232
Notes payable, net 140,490 99,129
Total liabilities 325,696 238,299
Fair Value | Fair Value, Measurements, Nonrecurring | Level 1    
Assets    
Cash and cash equivalents 204,847 172,103
Notes receivable, net 0 0
Other receivables, net 0 0
Total assets 204,847 172,103
Liabilities    
Accrued compensation 0 0
Commissions and fees payable 0 0
Accounts payable and accrued liabilities 0 0
Accrued interest 0 0
Notes payable, net 0 0
Total liabilities 0 0
Fair Value | Fair Value, Measurements, Nonrecurring | Level 2    
Assets    
Cash and cash equivalents 0 0
Notes receivable, net 5,893 47,369
Other receivables, net 129,182 60,707
Total assets 182,608 159,441
Liabilities    
Accrued compensation 27,418 33,343
Commissions and fees payable 105,194 67,221
Accounts payable and accrued liabilities 52,403 38,374
Accrued interest 191 232
Notes payable, net 140,490 99,129
Total liabilities 325,696 238,299
Receivables from clearing brokers | Carrying Value | Fair Value, Measurements, Nonrecurring    
Assets    
Receivables 45,013 48,543
Receivables from clearing brokers | Fair Value | Fair Value, Measurements, Nonrecurring    
Assets    
Receivables 45,013 48,543
Receivables from clearing brokers | Fair Value | Fair Value, Measurements, Nonrecurring | Level 1    
Assets    
Receivables 0 0
Receivables from clearing brokers | Fair Value | Fair Value, Measurements, Nonrecurring | Level 2    
Assets    
Receivables 45,013 48,543
Receivables from other broker-dealers | Carrying Value | Fair Value, Measurements, Nonrecurring    
Assets    
Receivables 2,520 2,822
Receivables from other broker-dealers | Fair Value | Fair Value, Measurements, Nonrecurring    
Assets    
Receivables 2,520 2,822
Receivables from other broker-dealers | Fair Value | Fair Value, Measurements, Nonrecurring | Level 1    
Assets    
Receivables 0 0
Receivables from other broker-dealers | Fair Value | Fair Value, Measurements, Nonrecurring | Level 2    
Assets    
Receivables $ 2,520 $ 2,822