Long-Term Debt, Net - Additional Information (Details)					1 Months Ended		6 Months Ended	12 Months Ended
	Feb. 18, 2020 USD ($) day $ / shares	Feb. 13, 2020 USD ($) shares	May 09, 2019 USD ($)	Oct. 31, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jul. 31, 2017 USD ($) shares	Sep. 30, 2020 USD ($) $ / shares	Sep. 30, 2020 USD ($) $ / shares	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Jun. 25, 2018 USD ($)	Oct. 30, 2017 USD ($)	Sep. 30, 2017 USD ($) $ / shares	Dec. 31, 2014 USD ($) shares	Dec. 31, 2013 USD ($) creditor shares
Debt Instrument [Line Items]
Proceeds from borrowings on exchangeable notes								$ 138,000,000	$ 0	$ 0
Equity component of exchangeable notes, net of issuance costs and deferred taxes								27,578,000
Debt issuance costs incurred			$ 152,000
Debt issuance costs							$ 4,212,000	4,212,000	1,245,000
Amortization of deferred debt issuance costs								758,000	721,000	1,072,000
Debt issuance costs, net							4,567,000	4,567,000	1,846,000
Exchangeable notes, fair value							102,064,000	102,064,000
Repayments of convertible debt								17,414,000	0	0
Debt issuance cost write offs								141,000	152,000	0
Payments for note hedge transactions	$ 28,676,000							28,676,000	0	0
Proceeds from issuance of warrants								14,669,000	0	0
Conversion of notes payable to related and unrelated creditors to Class A common stock								0	$ 0	$ 8,054,000
1.0% Exchangeable Senior Notes due 2025
Debt Instrument [Line Items]
Repayments of convertible debt							17,414,000
1.0% Exchangeable Senior Notes due 2025 | Exchangeable Notes
Debt Instrument [Line Items]
Original principal amount	$ 138,000,000
Stated interest rate (percent)	1.00%
Proceeds from borrowings on exchangeable notes	$ 132,762,000
Debt issuance costs incurred	5,238,000
Debt issuance costs	$ 4,150,000
Amortization of deferred debt issuance costs								365,000
Debt issuance costs, net							3,193,000	3,193,000
Debt aggregate repurchase amount							21,000,000	21,000,000
Debt interest, repurchase amount							24,000	$ 24,000
Loss on retirement of debt							2,297,000
Debt issuance cost write offs							$ 592,000
1.0% Exchangeable Senior Notes due 2025 | Exchangeable Notes | In Event of Fundamental Change
Debt Instrument [Line Items]
Repurchase price as percent of face value of notes (percent)	100.00%
1.0% Exchangeable Senior Notes due 2025 | Exchangeable Notes | February 20, 2023 to 47th Scheduled Trading Day Immediately Preceding the Maturity Date
Debt Instrument [Line Items]
Repurchase price as percent of face value of notes (percent)	100.00%
2020 Senior Secured Credit Facility | Line of Credit
Debt Instrument [Line Items]
Revolving line of credit borrowing capacity			275,000,000
Optional addition to borrowing capacity			50,000,000
Unused commitment fee (percent)								0.30%
Debt covenant, minimum consolidated interest coverage ratio							3.00	3.00
Debt covenant, maximum total leverage ratio							5.00	5.00
Debt covenant, maximum consolidated senior secured leverage ratio							3.25	3.25
Debt covenant, increase to maximum consolidated senior secured leverage ratio during leverage increase period							0.25	0.25
Remaining borrowing capacity							$ 275,000,000	$ 275,000,000
Debt covenant, equity repurchase limit from employees, directors, officers or consultants			$ 3,000,000
Debt covenant, dividend or distribution limit as percent of net cash proceeds from additional common equity issuance (percent)			5.00%
2020 Senior Secured Credit Facility | Line of Credit | Minimum
Debt Instrument [Line Items]
Unused commitment fee (percent)			0.15%
2020 Senior Secured Credit Facility | Line of Credit | Maximum
Debt Instrument [Line Items]
Unused commitment fee (percent)			0.30%
2020 Senior Secured Credit Facility | Line of Credit | One, Two, Three or Six-Month LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (percent)								3.25%
2020 Senior Secured Credit Facility | Line of Credit | One, Two, Three or Six-Month LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)			2.25%
2020 Senior Secured Credit Facility | Line of Credit | One, Two, Three or Six-Month LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)			3.25%
2020 Senior Secured Credit Facility | Line of Credit | Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on variable rate (percent)			0.50%
2020 Senior Secured Credit Facility | Line of Credit | LIBOR Plus 1%
Debt Instrument [Line Items]
Basis spread on variable rate (percent)			1.00%					1.25%
2020 Senior Secured Credit Facility | Line of Credit | LIBOR Plus 1% | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)			0.25%
2020 Senior Secured Credit Facility | Line of Credit | LIBOR Plus 1% | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)			1.25%
2020 Senior Secured Credit Facility | Line of Credit | Letter of Credit | Maximum
Debt Instrument [Line Items]
Unused commitment fee (percent)			3.25%
Term loans to bank under the Senior Secured Credit Facility | Secured Debt
Debt Instrument [Line Items]
Original principal amount												$ 40,000,000
Senior Secured Credit Facility | Line of Credit
Debt Instrument [Line Items]
Revolving line of credit borrowing capacity												$ 110,000,000
Quarterly principal payment				$ 1,250,000
Senior Secured Credit Facility | Line of Credit | Minimum
Debt Instrument [Line Items]
Unused commitment fee (percent)				0.15%
Senior Secured Credit Facility | Line of Credit | Maximum
Debt Instrument [Line Items]
Unused commitment fee (percent)				0.30%
Senior Secured Credit Facility | Line of Credit | Prime Rate | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)				0.50%
Senior Secured Credit Facility | Line of Credit | Prime Rate | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)				2.00%
Senior Secured Credit Facility | Line of Credit | 30-day LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)				2.75%
Senior Secured Credit Facility | Line of Credit | 30-day LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)				4.00%
Notes payable to Mezzanine Lenders | Notes Payable
Debt Instrument [Line Items]
Original principal amount															$ 10,500,000
Stated interest rate (percent)															12.00%
Debt issuance cost write offs					$ 78,000
Warrants outstanding (shares) | shares															1,423,688
Warrants sold in connection with the issuance of the Exchangeable notes (in USD per share) | $ / shares													$ 0.01
Number of creditors | creditor															3
Intrinsic value of warrants											$ 9,241,000		$ 767,000
Junior Subordinated Notes | Unsecured Debt
Debt Instrument [Line Items]
Original principal amount														$ 17,608,000
Stated interest rate (percent)														10.00%
Debt issuance cost write offs					43,000
Warrants outstanding (shares) | shares														1,433,920
Extinguishment of debt, amount					8,054,000
Additional Paid-In Capital
Debt Instrument [Line Items]
Equity component of exchangeable notes, net of issuance costs and deferred taxes	$ 28,662,000							$ 27,578,000
Additional Paid-In Capital | 1.0% Exchangeable Senior Notes due 2025 | Exchangeable Notes
Debt Instrument [Line Items]
Debt issuance costs	$ 1,088,000
Common Stock | Junior Subordinated Notes | Unsecured Debt
Debt Instrument [Line Items]
Loss on retirement of debt						$ 0
Conversion of notes payable to related and unrelated creditors to Class A common stock						$ 500,000
Debt conversion, converted instrument, shares issued | shares						148,000
Class A Common Stock
Debt Instrument [Line Items]
Exchangeable notes, exchange price per share (in USD per share) | $ / shares	$ 40.87						$ 40.87	$ 40.87
Warrants outstanding (shares) | shares		3,376,391
Warrants sold in connection with the issuance of the Exchangeable notes (in USD per share) | $ / shares							$ 62.88	$ 62.88
Proceeds from issuance of warrants		$ 14,669,000
Class A Common Stock | 1.0% Exchangeable Senior Notes due 2025 | Exchangeable Notes
Debt Instrument [Line Items]
Exchangeable notes, exchange rate, shares per $1000	0.0244666
Class A Common Stock | 1.0% Exchangeable Senior Notes due 2025 | Exchangeable Notes | February 20, 2023 to 47th Scheduled Trading Day Immediately Preceding the Maturity Date
Debt Instrument [Line Items]
Threshold exchange price as percent of closing price per share to allow redemption, (percent)	130.00%
Threshold trading days closing price for stock must exceed exchange price | day	20
Class A Common Stock | Common Stock
Debt Instrument [Line Items]
Conversion of notes payable to related and unrelated creditors to Class A common stock					$ 8,054,000