Long-term Debt (Tables)

6 Months Ended

Mar. 31, 2018

Debt Disclosure [Abstract]

Long term debt instruments

The following tables present our long-term debt instruments outstanding, contractual maturities and interest expense:

	March 31, 2018									March 31, 2017							September 30, 2017
	Gross Amount			Debt Discount and Issuance Costs			Carrying Amount			Gross Amount		Debt Discount and Issuance Costs			Carrying Amount		Gross Amount		Debt Discount and Issuance Costs			Carrying Amount
	(in thousands)
2019 Convertible Notes	$	195,000		$	(12,704	)	$	182,296		$	230,000	$	(26,536	)	$	203,464	$	195,000	$	(17,654	)	$	177,346
2019 Convertible Notes Embedded Derivative	16,042			—			16,042			15,138		—			15,138		6,591		—			6,591
2024 Convertible Notes	143,750			(40,463		)	103,287			—		—			—		143,750		(42,880		)	100,870
Term Loan Facility	—			—			—			50,000		(1,878		)	48,122		—		—			—
Total	$	354,792		$	(53,167	)	$	301,625		$	295,138	$	(28,414	)	$	266,724	$	345,341	$	(60,534	)	$	284,807
Less current portion	(143,750		)	40,463			(103,287		)	—		—			—		—		—			—
Total long-term debt	$	211,042		$	(12,704	)	$	198,338		$	295,138	$	(28,414	)	$	266,724	$	345,341	$	(60,534	)	$	284,807

Principal payment schedule

	Schedule of Contractual Maturities
	Total		Less Than 1 Year		1 - 3 Years		3 - 5 Years		More Than 5 Years
	(in thousands)
2019 Convertible Notes*	$	195,000	$	—	$	195,000	$	—	$	—
2024 Convertible Notes*	143,750		143,750		—		—		—
	$	338,750	$	143,750	$	195,000	$	—	$	—

* Excludes the potential impact of the embedded derivative.

Schedule of Interest Expense

	Three Months Ended March 31,				Six Months Ended March 31,
	2018		2017		2018		2017
	(in millions)
2019 Convertible Notes:
Contractual interest expense	$	1.1	$	1.3	$	2.1	$	2.5
Amortization of debt discount and deferred financing costs	2.4		2.7		5.0		5.5
Total interest expense	$	3.5	$	4.0	$	7.1	$	8.0
2024 Convertible Notes:
Contractual interest expense	$	1.0	$	—	$	2.0	$	—
Amortization of debt discount and deferred financing costs	1.3		—		2.5		—
Total interest expense	$	2.3	$	—	$	4.5	$	—