Long-Term Debt, Net - Additional Information (Details)				3 Months Ended		6 Months Ended
	Feb. 18, 2020 USD ($) numberOfDays	Feb. 13, 2020 USD ($) shares	Oct. 31, 2017 USD ($)	Mar. 31, 2020 USD ($) $ / shares	Mar. 31, 2019 USD ($)	Mar. 31, 2020 USD ($) $ / shares	Mar. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Oct. 30, 2017 USD ($)
Debt Instrument [Line Items]
Proceeds from borrowings on exchangeable notes						$ 138,000,000	$ 0
Equity component of exchangeable notes, net of issuance costs and deferred taxes				$ 27,569,000
Debt issuance costs, net				5,677,000		5,677,000		$ 1,846,000
Exchangeable notes, fair value				107,469,000		107,469,000
Payments for note hedge transactions	$ 28,676,000					28,676,000	0
Proceeds from issuance of warrants						14,669,000	0
Write off of unamortized debt issuance costs				141,000		141,000	0
Debt issuance costs incurred				152,000		152,000
Amortization of deferred debt issuance costs				172,000	$ 232,000	272,000	$ 465,000
Debt issuance costs				4,245,000		$ 4,245,000
Additional Paid-in Capital
Debt Instrument [Line Items]
Equity component of exchangeable notes, net of issuance costs and deferred taxes	28,662,000			$ 27,569,000
Class A Common Stock
Debt Instrument [Line Items]
Exchangeable notes, exchange price per share (in USD per share) | $ / shares				$ 40.87		$ 40.87
Proceeds from issuance of warrants		$ 14,669,000
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
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%
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)						0.25%
Remaining borrowing capacity				$ 256,000,000		$ 256,000,000
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%
Debt covenant, minimum consolidated interest coverage ratio				3.00		3.00
Debt covenant, maximum total leverage ratio				5.00		5.00
Debt covenant, increase to maximum total leverage ratio during leverage increase period				0.25		0.25
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
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 | Maximum | Letter of Credit
Debt Instrument [Line Items]
Unused commitment fee (percent)	3.25%
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)						2.75%
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%					0.75%
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%
1% 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	$ 132,721,000
Debt issuance costs, net				$ 4,113,000		$ 4,113,000
Debt issuance costs incurred	5,279,000
Amortization of deferred debt issuance costs				$ 70,000		$ 70,000
Debt issuance costs	4,183,000
1% Exchangeable Senior Notes due 2025 | Exchangeable Notes | Additional Paid-in Capital
Debt Instrument [Line Items]
Debt issuance costs	$ 1,096,000
1% Exchangeable Senior Notes due 2025 | Exchangeable Notes | Class A Common Stock
Debt Instrument [Line Items]
Exchangeable notes, exchange rate, shares per $1000	24.4666
1% 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% 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%
1% Exchangeable Senior Notes due 2025 | Exchangeable Notes | February 20, 2023 to 47th Scheduled Trading Day Immediately Preceding the Maturity Date | Class A Common Stock
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 | numberOfDays	20