Summary of Significant Accounting Policies - Stock-Based Compensation (Details)	1 Months Ended					3 Months Ended		6 Months Ended	9 Months Ended		12 Months Ended
	Jul. 31, 2019 shares	Apr. 30, 2019 item $ / shares shares	Jun. 30, 2017 item $ / shares shares	Feb. 28, 2017 item $ / shares shares	Aug. 31, 2016 item $ / shares shares	Sep. 30, 2019 USD ($) $ / shares shares	Sep. 30, 2018 USD ($) $ / shares	Jun. 30, 2019 USD ($) $ / shares shares	Sep. 30, 2019 USD ($) employee item $ / shares shares	Sep. 30, 2018 USD ($) $ / shares	Dec. 31, 2018 USD ($) $ / shares shares	Jun. 30, 2018 shares
Number of Stock Options
Outstanding at the beginning of the period (in shares)	3,700,000					3,700,000
Exercised (in shares)									(86,000)
Outstanding at the end of the period (in shares)								3,700,000
Stock plans disclosure
Cash received for exercise of stock options | $									$ 811,000	$ 2,943,000
Stock compensation expense | $								$ 2,800,000
ESPP
Weighted-average assumptions used to estimate the fair value of each stock option
Dividend (as a percent)								0.00%
Volatility (as a percent)								67.30%
Risk-free interest rate (as a percent)								2.51%
Expected life									5 years
Weighted-Average Grant Date Fair Value
Awarded (in dollars per share) | $ / shares								$ 1.63
Stock plans disclosure
Aggregate number of common shares reserved for future issuance												1,000,000
Estimated subscriptions outstanding								323,000
Stock compensation expense | $						$ 53,000	$ 213,000		$ 345,000	213,000
Stock options and restricted stock awards
Stock-Based Compensation
Vesting period									2 years
Stock plans disclosure
Stock compensation expense | $						3,600,000	$ 4,300,000		$ 10,700,000	$ 12,000,000.0
Estimated fair value that could be expensed | $						$ 23,800,000			$ 23,800,000
Stock options
Weighted-average assumptions used to estimate the fair value of each stock option
Dividend (as a percent)						0.00%	0.00%		0.00%	0.00%
Volatility (as a percent)						81.63%	71.91%		76.28%	70.99%
Risk-free interest rate (as a percent)						1.78%	2.89%		2.24%	2.72%
Expected life						6 years	6 years		6 years	6 years
Weighted-average grant date fair value (in dollars per share) | $ / shares						$ 1.68	$ 6.11		$ 2.85	$ 6.74
Number of Stock Options
Outstanding at the beginning of the period (in shares)								15,564,000	15,564,000
Granted (in shares)									7,340,000
Exercised (in shares)									(86,000)
Forfeited/Canceled (in shares)									(5,712,000)
Outstanding at the end of the period (in shares)						17,106,000			17,106,000		15,564,000
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share) | $ / shares								$ 10.20	$ 10.20
Granted (in dollars per share) | $ / shares									4.28
Exercised (in dollars per share) | $ / shares									2.53
Forfeited/Canceled (in dollars per share) | $ / shares									9.07
Outstanding at the end of the period (in dollars per share) | $ / shares						$ 8.08			$ 8.08		$ 10.20
Stock plans disclosure
Cash received for exercise of stock options | $									$ 217,000
Stock options | Minimum
Weighted-Average Exercise Price
Exercised (in dollars per share) | $ / shares									$ 1.84
Stock options | Maximum
Stock-Based Compensation
Vesting period									4 years
Exercise period									10 years
Weighted-Average Exercise Price
Exercised (in dollars per share) | $ / shares									$ 3.05
Performance shares
Stock-Based Compensation
Exercise period											5 years
Number of equal installments restrictions lapse | $											2
Number of Stock Options
Outstanding at the end of the period (in shares)						168,200			168,200
Number of Restricted Stock Shares
Awarded (in shares)											295,200
Stock plans disclosure
Stock compensation expense | $									$ 0
Estimated fair value that could be expensed | $						$ 850,000			$ 850,000
Restricted stock
Stock-Based Compensation
Number of equal installments restrictions lapse | item		3	3	3	3
Number of Restricted Stock Shares
Unvested at the beginning of the period (in shares)								1,816,000	1,816,000
Awarded (in shares)									631,000
Vested (in shares)									(504,000)
Forfeited (in shares)	(219,130)								(296,000)
Unvested at the end of the period (in shares)						1,647,000			1,647,000		1,816,000
Weighted-Average Grant Date Fair Value
Unvested at the beginning of the period (in dollars per share) | $ / shares								$ 2.87	$ 2.87
Awarded (in dollars per share) | $ / shares									2.55
Vested (in dollars per share) | $ / shares									2.64
Forfeited (in dollars per share) | $ / shares									2.56
Unvested at the end of the period (in dollars per share) | $ / shares						$ 2.88			$ 2.88		$ 2.87
Restricted stock | Officers
Number of Restricted Stock Shares
Awarded (in shares)		106,000	239,000	529,830	117,800
Weighted-Average Grant Date Fair Value
Awarded (in dollars per share) | $ / shares		$ 2.82	$ 4.71	$ 2.47	$ 3.15
Stock plans disclosure
Stock compensation expense | $									$ 0
Estimated fair value that could be expensed | $						$ 1,500,000			$ 1,500,000
2016 Plan
Stock-Based Compensation
Number of employee share-based compensation plans | employee									1
2016 Plan | Stock options
Weighted-average assumptions used to estimate the fair value of each stock option
Number of group of awards for which expected term is calculated for and applied | item									1
2018 Plan
Stock-Based Compensation
Common stock authorized for issuance (in shares)						7,500,000			7,500,000
Previous stock option plans
Stock-Based Compensation
Common stock authorized for issuance (in shares)						19,500,000			19,500,000