Income Taxes - Summary of Effective Income Tax Rate Reconciliation (Detail)	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
At U.S. federal statutory rate	35.00%	21.00%	34.00%
State taxes, net of federal effect		7.90%	4.90%
Stock compensation		2.60%	(5.80%)
Mark-to-market adjustments		0.20%	0.90%
Valuation allowance		36.20%	(23.10%)
True-up on deferred taxes			(3.00%)
State blended rate change			(5.70%)
Federal tax rate change in 2018		(67.90%)
Other			(2.20%)
Effective income tax rate		0.00%	0.00%