Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Statement of Financial Position [Abstract]
Accounts receivable, allowances	$ 1,029	$ 980
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	52,435,000	51,934,000
Common stock, shares outstanding (in shares)	33,293,000	33,464,000
Treasury stock, shares (in shares)	19,142,000	18,470,000