Debt - Outstanding Obligations (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018	May 14, 2018	Jul. 31, 2017	Jun. 30, 2014
Gross Amount
Total	$ 317,696	$ 317,976	$ 513,668
Less current portion	215	214	195,162
Total long-term debt	317,481	317,762	318,506
Debt Discount and Issuance Costs
Total	(76,272)	(79,382)	(93,502)
Less current portion	0	0	(4,924)
Total long-term debt	(76,272)	(79,382)	(88,578)
Carrying Amount
Total	241,424	238,594	420,166
Less current portion	215	214	190,238
Total long-term debt	241,209	238,380	229,928
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	(4,924)
Carrying Amount
Total	0	0	190,076
Senior Notes | 2019 Convertible Notes Embedded Derivative
Gross Amount
Total	0	0	21
Debt Discount and Issuance Costs
Total	0	0	0
Carrying Amount
Total	0	0	21
Senior Notes | 2024 Convertible Notes
Gross Amount
Total	143,750	143,750	143,750
Debt Discount and Issuance Costs
Total	(31,010)	(32,439)	(36,568)
Carrying Amount
Total	112,740	111,311	107,182
Senior Notes | 2025 Convertible Notes
Gross Amount
Total	172,500	172,500	172,500
Debt Discount and Issuance Costs
Total	(44,598)	(46,290)	(51,184)
Carrying Amount
Total	127,902	126,210	121,316
Stated interest rate				2.375%
Unsecured Debt | 8.5% unsecured debt due 2024
Gross Amount
Total	1,042	1,092	1,237
Debt Discount and Issuance Costs
Total	0	0	0
Carrying Amount
Total	$ 1,042	1,092	1,237
Stated interest rate	8.50%
Receivables Securitization Facility | CASHMAX secured borrowing facility
Gross Amount
Total	$ 404	634	1,160
Debt Discount and Issuance Costs
Total	(664)	(653)	(826)
Carrying Amount
Total	$ (260)	$ (19)	$ 334