Stock-Based Compensation - Restricted Stock (Details) - Restricted stock $ / shares in Units, $ in Millions	3 Months Ended
	Dec. 31, 2016 USD ($) $ / shares shares
Common-stock based award plan
Unrecognized compensation cost (in dollars) | $	$ 34.4
Weighted-average period over which unrecognized compensation cost is expected to be recognized	2 years 10 months 24 days
Restricted stock awards activity, shares
Unvested at the beginning of the period (in shares) | shares	648,000
Granted (in shares) | shares	263,362
Vested (in shares) | shares	(270,000)
Forfeited (in shares) | shares	(2,000)
Unvested at the end of the period (in shares) | shares	639,000
Restricted stock awards activity, weighted average grant date fair value
Unvested at the beginning of the period (in dollars per share) | $ / shares	$ 64.24
Granted (in dollars per share) | $ / shares	81.31
Vested (in dollars per share) | $ / shares	63.79
Forfeited/Expired (in dollars per share) | $ / shares	66.73
Unvested at the end of the period (in dollars per share) | $ / shares	$ 71.46
Minimum
Common-stock based award plan
Vesting period	3 years
Maximum
Common-stock based award plan
Vesting period	6 years