Stock-based Compensation - Nonvested Stock Awards (Details)	9 Months Ended
	Jun. 30, 2018 $ / shares shares
Restricted Stock
Shares
Beginning of period (in shares) | shares	1,540,947
Granted (in shares) | shares	442,250
Vested (in shares) | shares	(277,611)
Forfeited (in shares) | shares	(209,701)
End of period (in shares) | shares	1,495,885
Weighted Average Grant Date Fair Value
Beginning of period (in dollars per share) | $ / shares	$ 16.14
Granted (in dollars per share) | $ / shares	20.26
Vested (in dollars per share) | $ / shares	15.07
Forfeited (in dollars per share) | $ / shares	18.71
End of period (in dollars per share) | $ / shares	$ 17.20
Performance-Based Restricted Stock Awards
Shares
Beginning of period (in shares) | shares	668,766
Granted (in shares) | shares	165,085
Vested (in shares) | shares	0
Forfeited (in shares) | shares	(188,058)
End of period (in shares) | shares	645,793
Weighted Average Grant Date Fair Value
Beginning of period (in dollars per share) | $ / shares	$ 15.72
Granted (in dollars per share) | $ / shares	22.40
Vested (in dollars per share) | $ / shares	0.00
Forfeited (in dollars per share) | $ / shares	18.96
End of period (in dollars per share) | $ / shares	$ 16.48
Time Based Restricted Stock Awards
Shares
Beginning of period (in shares) | shares	872,181
Granted (in shares) | shares	277,165
Vested (in shares) | shares	(277,611)
Forfeited (in shares) | shares	(21,643)
End of period (in shares) | shares	850,092
Weighted Average Grant Date Fair Value
Beginning of period (in dollars per share) | $ / shares	$ 16.47
Granted (in dollars per share) | $ / shares	18.98
Vested (in dollars per share) | $ / shares	15.07
Forfeited (in dollars per share) | $ / shares	16.52
End of period (in dollars per share) | $ / shares	$ 17.75