Debt - Outstanding Obligations (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019	May 31, 2018	May 14, 2018	Jul. 31, 2017
Gross Amount
Total	$ 317,066	$ 317,122	$ 317,696
Less current portion	213	213	215
Total long-term debt	316,853	316,909	317,481
Debt Discount and Issuance Costs
Total	(62,531)	(65,893)	(76,272)
Less current portion	0	0	0
Total long-term debt	(62,531)	(65,893)	(76,272)
Carrying Amount
Total	254,535	251,229	241,424
Less current portion	213	213	215
Total long-term debt	254,322	251,016	241,209
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	(25,014)	(26,557)	(31,010)
Carrying Amount
Total	118,736	117,193	112,740
Senior Notes | 2025 Convertible Notes
Gross Amount
Total	172,500	172,500	172,500
Debt Discount and Issuance Costs
Total	(37,517)	(39,336)	(44,598)
Carrying Amount
Total	134,983	133,164	127,902
Unsecured Debt | 8.5% unsecured debt due 2024
Gross Amount
Total	816	872	1,042
Debt Discount and Issuance Costs
Total	0	0	0
Carrying Amount
Total	$ 816	872	1,042
Stated interest rate	8.50%
Receivables Securitization Facility | CASHMAX secured borrowing facility
Gross Amount
Total	$ 0	0	404
Debt Discount and Issuance Costs
Total	0	0	(664)
Carrying Amount
Total	$ 0	$ 0	$ (260)