Stock-based Compensation - Stock Options Outstanding (Details)	3 Months Ended	6 Months Ended
	Mar. 31, 2018 $ / shares shares	Mar. 31, 2018 $ / shares shares
Shares
Exercised (shares) | shares		(1,666)
Weighted Average Exercise Price
Exercised (in dollars per share) | $ / shares		$ 7.56
Stock Options
Shares
Outstanding at beginning of period (shares) | shares	556,159	593,753
Granted (shares) | shares	0	23,680
Exercised (shares) | shares	0
Expired (shares) | shares	0	(56,967)
Forfeited (shares) | shares	(5,900)	(8,541)
Outstanding at end of period (shares) | shares	550,259	550,259
Exercisable at end of period (shares) | shares	435,432	435,432
Vested or expected to vest in the future (shares) | shares	550,222	550,222
Weighted Average Exercise Price
Outstanding at beginning of period (in dollars per share) | $ / shares	$ 14.11	$ 14.76
Granted (in dollars per share) | $ / shares	0.00	20.46
Exercised (in dollars per share) | $ / shares	0.00
Expired (in dollars per share) | $ / shares	0.00	23.65
Forfeited (in dollars per share) | $ / shares	7.48	9.46
Outstanding at end of period (in dollars per share) | $ / shares	14.18	14.18
Exercisable at end of period (in dollars per share) | $ / shares	14.81	14.81
Vested or expected to vest in the future (in dollars per share) | $ / shares	$ 14.18	$ 14.18