Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018
Statement Of Financial Position [Abstract]
Accounts receivable, allowances	$ 13,095	$ 17,584
Convertible preferred stock, par value	$ 0.01	$ 0.01
Convertible preferred stock. aggregate liquidation preference	$ 400,000	$ 400,000
Convertible preferred stock, shares authorized	400,000	400,000
Convertible preferred stock, shares issued	400,000	400,000
Convertible preferred stock, shares outstanding	400,000	400,000
Common stock (voting), par value	$ 0.01	$ 0.01
Common stock (voting), shares authorized	100,000,000	100,000,000
Common Stock (voting), issued	68,574,176	68,135,790
Common Stock (voting), outstanding	68,574,176	68,135,790
Undesignated Preferred Stock, shares authorized	5,000,000	5,000,000
Undesignated Preferred Stock, issued	0	0
Undesignated Preferred Stock, outstanding	0	0