Long-Term Debt (Details) - USD ($)	Sep. 30, 2019	Dec. 31, 2018	Jun. 30, 2017	Mar. 31, 2016
Debt Instrument [Line Items]
Long-term debt net of current maturities	$ 222,281,000	$ 225,733,000
Convertible Subordinated Debt | Convertible Senior Notes at 5.00% February 2021 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	134,000,000	150,000,000		$ 150,000,000
Long-term debt	122,100,000	130,260,000
Debt Instrument, Unamortized Discount	(10,356,000)	(17,193,000)
Debt Instrument, Fee Amount	(1,544,000)	(2,547,000)
Debt Instrument, Net Carrying Amount	122,100,000	130,260,000
Convertible Subordinated Debt | Convertible Senior Notes at 4.50% February 2022 [Domain]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	120,000,000	120,000,000	$ 120,000,000
Long-term debt	100,181,000	95,473,000
Debt Instrument, Unamortized Discount	(17,438,000)	(21,476,000)
Debt Instrument, Fee Amount	(2,381,000)	(3,051,000)
Debt Instrument, Net Carrying Amount	$ 100,181,000	$ 95,473,000