Convertible Senior Notes - Net proceeds (Details)		1 Months Ended	9 Months Ended
	Mar. 08, 2018 USD ($)	Sep. 30, 2019 USD ($) D $ / shares	Sep. 30, 2019 USD ($) $ / shares	Sep. 30, 2018 USD ($)	Mar. 31, 2019 $ / shares	Mar. 31, 2018 USD ($)
Convertible Senior Notes
Principal amount		$ 100,000,000	$ 100,000,000
Proceeds from issuance of debt			39,052,000	$ 95,856,000
Unamortized debt discount and issuance costs		900,000	900,000
Closing price of the company's stock | $ / shares					$ 2.35
Convertible Senior Notes
Convertible Senior Notes
Principal amount		$ 40,000,000	$ 40,000,000
Interest rate (as a percent)		7.50%	7.50%
Proceeds from issuance of debt			$ 39,100,000
$40M Convertible Senior Note
Convertible Senior Notes
Principal amount		$ 40,000,000	$ 40,000,000
Interest rate (as a percent)		7.50%	7.50%
Proceeds from issuance of debt		$ 39,100,000
Percentage of principal amount to be repaid at maturity		120.00%
Maturity principal amount		$ 48,000,000	$ 48,000,000
Conversion rates for the notes (in shares)		387.5969
Conversion price, per share | $ / shares		$ 2.58	$ 2.58
Consecutive trading days | D		20
Conversion price (as a percent)		175.00%
Transaction costs for issuance		$ 8,000,000	$ 8,000,000
Initial purchasers' discount		8,000,000
Remaining life of the Convertible Senior Notes			40 months
$40M Convertible Senior Note | Holder may require redemption
Convertible Senior Notes
Principal amount		40,000,000	$ 40,000,000
Maturity principal amount		$ 48,000,000	48,000,000
Consecutive trading days | D		5
Principal amount of the repurchased Convertible Senior Notes(as a percent)		115.00%
Principal amount (as a percent)		110.00%
Conversion ratio, principal amount		$ 1,000	1,000
$40M Convertible Senior Note | Company may redeem with the consent of the holder
Convertible Senior Notes
Principal amount		40,000,000	40,000,000
Maturity principal amount		$ 48,000,000	48,000,000
Principal amount of the repurchased Convertible Senior Notes(as a percent)		105.00%
Principal amount (as a percent)		115.00%
Conversion ratio, principal amount		$ 1,000	1,000
$100M Convertible Senior Notes
Convertible Senior Notes
Principal amount		$ 100,000,000	$ 100,000,000			$ 100,000,000
Interest rate (as a percent)		5.50%	5.50%			5.50%
Proceeds from issuance of debt			$ 52,356,000
Conversion rates for the notes (in shares)		436.3002
Conversion price, per share | $ / shares		$ 2.29	$ 2.29
Trading days | D		20
Consecutive trading days | D		30
Conversion price (as a percent)		130.00%
Number of business days		5 days
Number of consecutive trading days		5 days
Principal amount (as a percent)		98.00%
Ownership interest percentage		50.00%	50.00%
Percentage of principal amount to be redeemed		100.00%
Carrying amount of the liability component		$ 58,200,000	$ 58,200,000
Carrying amount of the equity component		$ 37,702,000	$ 37,702,000
Effective interest rate (as a percent)		16.00%	16.00%
Transaction costs for issuance		$ 4,100,000	$ 4,100,000
Initial purchasers' discount	$ 3,300,000
Other issuance costs	$ 900,000	1,700,000
Transaction costs attributable to the liability component		2,400,000
Transaction costs attributable to the equity component		$ 1,700,000
Remaining life of the Convertible Senior Notes		42 years
Closing price of the company's stock | $ / shares		$ 2.63	$ 2.63