Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2019	Sep. 30, 2018
Statement Of Financial Position [Abstract]
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, Authorized shares	500,000,000	500,000,000
Common stock, shares issued	116,986,000	120,145,000
Common stock, shares outstanding	116,725,000	119,926,000
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, Authorized shares	50,000,000	50,000,000
Preferred stock, shares issued	0	0