Stock-based Compensation (Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding and Exercisable) (Details) (Options, USD $) In Thousands, except Per Share data, unless otherwise specified	6 Months Ended
	Mar. 31, 2015
Options
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding at September 30, 2014	4,240
Granted	85
Exercised	(733)
Cancelled/Expired	(36)
Outstanding at March 31, 2015	3,556
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Outstanding at September 30, 2014	$ 8.10
Granted	$ 14.83
Exercised	$ 7.53
Cancelled/Expired	$ 10.07
Outstanding at March 31, 2015	$ 8.35
Aggregate Intrinsic Value, options exercised	$ 6,456
Weighted-Average Remaining Contractual Term in Years, Outstanding at March 31, 2015 (years)	3 years 5 months 23 days
Aggregate Intrinsic Value, Outstanding at March 31, 2015	33,906
Number of Shares, Exercisable at March 31, 2015 (shares)	2,473
Weighted-Average Exercise Price, Exercisable at March 31, 2015	$ 7.39
Weighted-Average Remaining Contractual Term in Years, Exercisable at March 31, 2015 (years)	2 years 10 months 6 days
Aggregate Intrinsic Value, Exercisable at March 31, 2015	25,963
Number of Shares, Vested and expected to vest after March 31, 2015 (shares)	3,515
Weighted-Average Exercise Price, Vested and expected to vest after March 31, 2015	$ 8.32
Weighted-Average Remaining Contractual Term in Years, Vested and expected to vest after March 31, 2015 (years)	3 years 5 months 16 days
Aggregate Intrinsic Value, Vested and expected to vest after March 31, 2015	$ 33,626