Fair Value of Assets and Liabilities - Carrying Values and Estimated Fair Values of Financial Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Liabilities
Contingent consideration liability	$ 744	$ 311	$ 424	$ 534
Carrying Value | Fair Value, Measurements, Nonrecurring
Assets
Receivables from broker-dealers and clearing organizations	3,967	2,850
Forgivable loans receivable	1,567	1,616
Other Receivables, Net	4,265	5,180
Total assets	38,055	34,195
Liabilities
Accrued commissions and payroll payable	12,862	10,065
Accounts payable and accrued expenses	7,275	8,404
Total liabilities	20,137	18,469
Total Estimated Fair Value | Fair Value, Measurements, Nonrecurring
Assets
Receivables from broker-dealers and clearing organizations	3,967	2,850
Forgivable loans receivable	1,567	1,616
Other Receivables, Net	4,265	5,180
Total assets	38,055	34,195
Liabilities
Accrued commissions and payroll payable	12,862	10,065
Accounts payable and accrued expenses	7,275	8,404
Total liabilities	20,137	18,469
Total Estimated Fair Value | Fair Value, Measurements, Nonrecurring | Level 1
Assets
Receivables from broker-dealers and clearing organizations	0	0
Forgivable loans receivable	0	0
Other Receivables, Net	0	0
Total assets	28,256	24,549
Liabilities
Accrued commissions and payroll payable	0	0
Accounts payable and accrued expenses	0	0
Total liabilities	0	0
Total Estimated Fair Value | Fair Value, Measurements, Nonrecurring | Level 2
Assets
Receivables from broker-dealers and clearing organizations	3,967	2,850
Forgivable loans receivable	1,567	1,616
Other Receivables, Net	4,265	5,180
Total assets	9,799	9,646
Liabilities
Accrued commissions and payroll payable	12,862	10,065
Accounts payable and accrued expenses	7,275	8,404
Total liabilities	20,137	18,469
Cash | Carrying Value | Fair Value, Measurements, Nonrecurring
Assets
Cash and cash equivalents	27,920	23,508
Cash | Total Estimated Fair Value | Fair Value, Measurements, Nonrecurring
Assets
Cash and cash equivalents	27,920	23,508
Cash | Total Estimated Fair Value | Fair Value, Measurements, Nonrecurring | Level 1
Assets
Cash and cash equivalents	27,920	23,508
Cash | Total Estimated Fair Value | Fair Value, Measurements, Nonrecurring | Level 2
Assets
Cash and cash equivalents	0	0
Cash deposits with clearing organizations | Carrying Value | Fair Value, Measurements, Nonrecurring
Assets
Cash and cash equivalents	336	1,041
Cash deposits with clearing organizations | Total Estimated Fair Value | Fair Value, Measurements, Nonrecurring
Assets
Cash and cash equivalents	336	1,041
Cash deposits with clearing organizations | Total Estimated Fair Value | Fair Value, Measurements, Nonrecurring | Level 1
Assets
Cash and cash equivalents	336	1,041
Cash deposits with clearing organizations | Total Estimated Fair Value | Fair Value, Measurements, Nonrecurring | Level 2
Assets
Cash and cash equivalents	$ 0	$ 0