Debt - Outstanding Obligations (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Sep. 30, 2019	Mar. 31, 2019	May 14, 2018	Jul. 31, 2017	Jun. 30, 2014
Gross Amount
Total	$ 317,514	$ 317,976	$ 513,546
Less current portion	267	214	195,213
Total long-term debt	317,247	317,762	318,333
Debt Discount and Issuance Costs
Total	(72,959)	(79,382)	(87,912)
Less current portion	0	0	(2,312)
Total long-term debt	(72,959)	(79,382)	(85,600)
Carrying Amount
Total	244,555	238,594	425,634
Less current portion	267	214	192,901
Total long-term debt	244,288	238,380	232,733
2019 Convertible Notes
Carrying Amount
Stated interest rate						2.125%
2024 Convertible Notes
Carrying Amount
Stated interest rate					2.875%
Senior Notes | 2019 Convertible Notes
Gross Amount
Total	0	0	195,000
Debt Discount and Issuance Costs
Total	0	0	(2,312)
Carrying Amount
Total	0	0	192,688
Senior Notes | 2024 Convertible Notes
Gross Amount
Total	143,750	143,750	143,750
Debt Discount and Issuance Costs
Total	(29,554)	(32,439)	(35,217)
Carrying Amount
Total	114,196	111,311	108,533
Senior Notes | 2025 Convertible Notes
Gross Amount
Total	172,500	172,500	172,500
Debt Discount and Issuance Costs
Total	(42,876)	(46,290)	(49,582)
Carrying Amount
Total	129,624	126,210	122,918
Stated interest rate				2.375%
Unsecured Debt | 8.5% unsecured debt due 2024
Gross Amount
Total	983	1,092	1,191
Debt Discount and Issuance Costs
Total	0	0	0
Carrying Amount
Total	$ 983	1,092	1,191
Stated interest rate	8.50%
Receivables Securitization Facility | CASHMAX secured borrowing facility
Gross Amount
Total	$ 281	634	1,105
Debt Discount and Issuance Costs
Total	(529)	(653)	(801)
Carrying Amount
Total	$ (248)	$ (19)	$ 304