Long-Term Debt Components of Convertible Debt (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2017	Mar. 31, 2016
Debt Instrument [Line Items]
Issuance of warrants					$ 12,376,000
Long-term debt	$ 244,243,000		$ 219,522,000
Convertible Subordinated Debt | Convertible Senior Notes at 5.00% February 2021 [Member]
Debt Instrument [Line Items]
Debt Instrument, Increase, Accrued Interest	745,000	$ 1,875,000
Debt Instrument, Face Amount	$ 61,091,000		61,091,000				$ 150,000,000
Interest rate (as a percent)	5.00%
Unamortized discount	$ (3,092,000)		(3,916,000)
Long-term debt	57,573,000		56,628,000
Debt Instrument, Fee Amount	(426,000)		(547,000)
Debt Instrument, Net Carrying Amount	57,573,000		56,628,000
Convertible Subordinated Debt | Convertible Senior Notes at 4.50% February 2022 [Domain]
Debt Instrument [Line Items]
Debt Instrument, Increase, Accrued Interest	1,350,000	$ 1,350,000
Debt Instrument, Face Amount	$ 120,000,000		120,000,000			$ 120,000,000
Issuance of warrants				$ 14,100,000
Interest rate (as a percent)	4.50%
Unamortized discount	$ (14,566,000)		(16,027,000)
Long-term debt	103,499,000		101,815,000
Debt Instrument, Fee Amount	(1,935,000)		(2,158,000)
Debt Instrument, Net Carrying Amount	103,499,000		101,815,000
Convertible Subordinated Debt | Convertible Senior Notes at 5.00% November 2024 [Domain]
Debt Instrument [Line Items]
Long-term debt	61,325,000		60,817,000
Convertible Subordinated Debt | Convertible Senior Notes at 5.00% November 2024 [Member]
Debt Instrument [Line Items]
Debt Instrument, Increase, Accrued Interest	911,000
Debt Instrument, Loss on Exchange			5,885,000
Debt Instrument, Face Amount	$ 72,909,000		$ 72,909,000
Interest rate (as a percent)	5.00%		5.00%
Unamortized discount	$ (10,285,000)		$ (10,733,000)
Debt Instrument, Fee Amount	(1,299,000)		(1,359,000)
Debt Instrument, Net Carrying Amount	$ 61,325,000		$ 60,817,000