Summary of Significant Accounting Policies - Narrative (Details)	1 Months Ended	12 Months Ended
	Feb. 28, 2015	Sep. 30, 2015 USD ($) $ / shares	Sep. 30, 2014 USD ($) $ / shares
Class of Stock [Line Items]
Duration between trade date and final settlement		90 days
Ownership percentage in an inactive subsidiary		24.90%
Anti-dilutive common shares outstanding (in shares) | $ / shares		$ 1,328,000
Deferred clearing rebates recognized		$ 184,000	$ 134,000
Deferred clearing rebates		821,000	971,000
Deferred marketing rebates recognized		16,000	0
Deferred marketing rebates		384,000	0
Reimbursement of expenses		$ 11,637,000	$ 9,973,000
Stock options
Class of Stock [Line Items]
Anti-dilutive common shares outstanding (in shares) | $ / shares			$ 682,700
Common Stock
Class of Stock [Line Items]
Reverse stock split (ratio)	0.1