Debt - Outstanding Obligations (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Sep. 30, 2020	Jun. 30, 2020	May 31, 2018	May 14, 2018	Jul. 31, 2017
Gross Amount
Total	$ 316,250	$ 317,122	$ 317,543
Less current portion	0	213	268
Total long-term debt	316,250	316,909	317,275
Debt Discount and Issuance Costs
Total	(55,618)	(65,893)	(69,657)
Less current portion	0	0	0
Total long-term debt	(55,618)	(65,893)	(69,657)
Carrying Amount
Total	260,632	251,229	247,886
Less current portion	0	213	268
Total long-term debt	260,632	251,016	247,618
2024 Convertible Notes
Carrying Amount
Stated interest rate						2.875%
2025 Convertible Notes
Carrying Amount
Stated interest rate				2.375%	2.375%
Senior Notes | 2024 Convertible Notes
Gross Amount
Total	143,750	143,750	143,750
Debt Discount and Issuance Costs
Total	(21,840)	(26,557)	(28,069)
Carrying Amount
Total	121,910	117,193	115,681
Senior Notes | 2025 Convertible Notes
Gross Amount
Total	172,500	172,500	172,500
Debt Discount and Issuance Costs
Total	(33,778)	(39,336)	(41,122)
Carrying Amount
Total	138,722	133,164	131,378
Unsecured Debt | 8.5% unsecured debt due 2024
Gross Amount
Total	0	872	998
Debt Discount and Issuance Costs
Total	0	0	0
Carrying Amount
Total	$ 0	872	998
Stated interest rate	8.50%
Receivables Securitization Facility | CASHMAX secured borrowing facility
Gross Amount
Total	$ 0	0	295
Debt Discount and Issuance Costs
Total	0	0	(466)
Carrying Amount
Total	$ 0	$ 0	$ (171)