Annual report pursuant to Section 13 and 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
Dec. 31, 2017
Dec. 31, 2016
Liabilities    
Contingent consideration payable $ 2,104 $ 7,144
Carrying Value | Fair Value, Measurements, Nonrecurring    
Assets    
Cash and cash equivalents 172,103 98,930
Notes receivable, net 46,778 32,611
Other receivables, net 60,707 54,634
Total assets 330,953 228,520
Liabilities    
Accrued compensation 33,343 26,299
Commissions and fees payable 67,221 60,594
Accounts payable and accrued liabilities 38,374 32,732
Accrued interest 232 281
Notes payable, net 96,849 26,417
Total liabilities 236,019 146,323
Fair Value | Fair Value, Measurements, Nonrecurring    
Assets    
Cash and cash equivalents 172,103 98,930
Notes receivable, net 46,778 32,611
Other receivables, net 60,707 54,634
Total assets 330,953 228,520
Liabilities    
Accrued compensation 33,343 26,299
Commissions and fees payable 67,221 60,594
Accounts payable and accrued liabilities 38,374 32,732
Accrued interest 232 281
Notes payable, net 99,129 24,494
Total liabilities 238,299 144,400
Fair Value | Fair Value, Measurements, Nonrecurring | Level 1    
Assets    
Cash and cash equivalents 172,103 98,930
Notes receivable, net 0 0
Other receivables, net 0 0
Total assets 172,103 98,930
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 46,778 32,611
Other receivables, net 60,707 54,634
Total assets 158,850 129,590
Liabilities    
Accrued compensation 33,343 26,299
Commissions and fees payable 67,221 60,594
Accounts payable and accrued liabilities 38,374 32,732
Accrued interest 232 281
Notes payable, net 99,129 24,494
Total liabilities 238,299 144,400
Receivables from clearing brokers | Carrying Value | Fair Value, Measurements, Nonrecurring    
Assets    
Receivables 48,543 41,492
Receivables from clearing brokers | Fair Value | Fair Value, Measurements, Nonrecurring    
Assets    
Receivables 48,543 41,492
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 48,543 41,492
Receivables from other broker-dealers | Carrying Value | Fair Value, Measurements, Nonrecurring    
Assets    
Receivables 2,822 853
Receivables from other broker-dealers | Fair Value | Fair Value, Measurements, Nonrecurring    
Assets    
Receivables 2,822 853
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 $ 2,822 $ 853