CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Jun. 30, 2020	Sep. 30, 2019
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Class A Common Stock
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	400,000,000	400,000,000
Common stock, shares issued (in shares)	33,430,364	32,597,736
Common stock, shares outstanding (in shares)	33,430,364	32,597,736
Class B Common Stock
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares issued (in shares)	21,274,333	22,106,961
Common stock, shares outstanding (in shares)	18,351,381	19,184,009
Treasury stock, shares (in shares)	2,922,952	2,922,952