Net Loss Per Share - Antidilutive (Details) - shares	Sep. 30, 2017	Sep. 30, 2016
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from net loss per share (shares)	22,387,029	23,323,728
Stock options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from net loss per share (shares)	7,896,734	10,736,433
Unvested restricted stock units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from net loss per share (shares)	13,241,111	11,210,178
ESPP shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from net loss per share (shares)	262,007	271,174
Stock Settled Bonus Shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from net loss per share (shares)	987,177	1,105,943
ESPP and stock-settled bonus plans | Adjustment
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from net loss per share (shares)		1,400,000