Long-Term Debt - Debt (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2016
Debt Instrument [Line Items]
Long-term debt	$ 219,522,000	$ 225,733,000
Less current maturities of long-term debt	(58,000)	0
Long-term debt of current maturities	219,464,000	225,733,000
Convertible Subordinated Debt | Convertible Senior Notes at 5.00% February 2021
Debt Instrument [Line Items]
Debt Instrument, Face Amount	61,091,000	150,000,000	$ 150,000,000
Long-term debt	56,628,000	130,260,000
Debt Instrument, Unamortized Discount	(3,916,000)	(17,193,000)
Debt Instrument, Fee Amount, Net Balance Shown as a Liability	(547,000)	(2,547,000)
Debt Instrument, Net Carrying Amount	56,628,000	130,260,000
Convertible Subordinated Debt | Convertible Senior Notes at 4.50% February 2022
Debt Instrument [Line Items]
Debt Instrument, Face Amount	120,000,000	120,000,000
Long-term debt	101,815,000	95,473,000
Debt Instrument, Unamortized Discount	(16,027,000)	(21,476,000)
Debt Instrument, Fee Amount, Net Balance Shown as a Liability	(2,158,000)	(3,051,000)
Debt Instrument, Net Carrying Amount	101,815,000	95,473,000
Convertible Subordinated Debt | Convertible Senior Notes at 5.00% February 2024
Debt Instrument [Line Items]
Debt Instrument, Face Amount	72,909,000
Long-term debt	60,817,000	0
Debt Instrument, Unamortized Discount	(10,733,000)
Debt Instrument, Fee Amount, Net Balance Shown as a Liability	(1,359,000)
Debt Instrument, Net Carrying Amount	60,817,000
Other obligations
Debt Instrument [Line Items]
Long-term debt	$ 262,000	$ 0