Share Based Compensation - Stock Option Activity (Details) - USD ($)			6 Months Ended
	Mar. 31, 2018	Sep. 30, 2017	Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Intrinsic value, exercises in period			$ 18,988
Options
Outstanding at beginning of the period (shares)			9,060,000
Granted (shares)			34,000
Exercised (shares)			(1,018,000)
Forfeited (shares)			(87,000)
Expired (shares)			0
Outstanding at end of the period (shares)	7,989,000	9,060,000	7,989,000
Options exercisable (shares)	5,516,000		5,516,000
Weighted Average Exercise Price/Share
Weighted average exercise price, outstanding, beginning balance (in dollars per share)			$ 5.18
Weighted average exercise price, granted (in dollars per share)			24.25
Weighted average exercise price, exercised (in dollars per share)			4.74
Weighted average exercise price, forfeited (in dollars per share)			7.65
Weighted average exercise price, expired (in dollars per share)			0.00
Weighted average exercise price, outstanding, ending balance (in dollars per share)	$ 5.29	$ 5.18	5.29
Weighted average exercise price, exercisable (in dollars per share)	$ 4.87		$ 4.87
Weighted Average Remaining Contractual Term
Weighted average remaining contractual term, outstanding	7 years 10 months 24 days	7 years 6 months
Weighted average contractual term, exercisable			6 years 6 months
Intrinsic value, outstanding	$ 10,045,000	$ 11,011,000	$ 10,045,000
Intrinsic value, exercisable	$ 5,569,000		$ 5,569,000