Stock-Based Compensation - Restricted Stock (Details) - Restricted stock $ / shares in Units, shares in Thousands, $ in Millions	9 Months Ended
	Jun. 30, 2018 USD ($) $ / shares shares
Stock based award plan
Unrecognized compensation cost (in dollars) | $	$ 41.0
Weighted-average period over which unrecognized compensation cost is expected to be recognized	2 years 6 months
Restricted stock awards activity, shares
Unvested at the beginning of the period (in shares) | shares	659
Granted (in shares) | shares	625
Vested (in shares) | shares	(258)
Forfeited (in shares) | shares	(19)
Unvested at the end of the period (in shares) | shares	1,007
Restricted stock awards activity, weighted average grant date fair value
Unvested at the beginning of the period (in dollars per share) | $ / shares	$ 70.76
Granted (in dollars per share) | $ / shares	59.52
Vested (in dollars per share) | $ / shares	71.16
Forfeited (in dollars per share) | $ / shares	68.98
Unvested at the end of the period (in dollars per share) | $ / shares	$ 63.72
Minimum
Stock based award plan
Vesting period	3 years
Maximum
Stock based award plan
Vesting period	6 years