Share-Based Payments - Restricted Stock Awards (Details) - Restricted Stock Awards - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Restricted stock (in shares)
Unvested at the beginning of the period (in shares)	446,000
Granted (in shares)	40,000	222,000	247,000
Vested (in shares)	(192,000)
Forfeited (in shares)	(23,000)
Unvested at the end of the period (in shares)	271,000	446,000
Restricted Stock (in dollars per share)
Unvested at the beginning of the period (in dollars per share)	$ 25.82
Granted (in dollars per share)	25.35
Vested (in dollars per share)	24.16
Forfeited (in dollars per share)	27.18
Unvested at the end of the period (in dollars per share)	$ 26.80	$ 25.82
Restricted stock (in years)
Weighted Average Remaining Vesting Term (in Years)	1 year 10 months 24 days	2 years 9 months 18 days
Total unrecognized compensation costs	$ 3.0
Weighted average period for recognition of unvested restricted awards	1 year 10 months 24 days
Executive management transition plan
Stock Awards
Granted (in shares)			210,820
Minimum
Restricted stock (in years)
Vesting period	3 years
Weighted average period for recognition of unvested restricted awards	3 years
Minimum | Executive management transition plan
Restricted stock (in years)
Vesting period			3 years
Maximum
Restricted stock (in years)
Vesting period	5 years
Weighted average period for recognition of unvested restricted awards	5 years
Maximum | Executive management transition plan
Restricted stock (in years)
Vesting period			4 years