Long-Term Debt (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016	Feb. 17, 2007
Debt Instrument [Line Items]
Long-term debt	$ 240,852,000	$ 161,349,000
Less current maturities of long-term debt	(1,940,000)	(15,261,000)
Long-term debt net of current maturities	238,912,000	146,088,000
Convertible Subordinated Debt | Convertible Senior Notes at 5.00% February 2021 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	150,000,000	150,000,000
Long-term debt	120,483,000	115,159,000
Debt Instrument, Unamortized Discount	(25,473,000)	(29,919,000)
Debt Instrument, Fee Amount	(4,044,000)	(4,922,000)
Debt Instrument, Net Carrying Amount	120,483,000	115,159,000
Convertible Subordinated Debt | Convertible Senior Notes at 4.50% February 2022 [Domain]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	120,000,000
Long-term debt	88,317,000	0
Debt Instrument, Unamortized Discount	(27,522,000)
Debt Instrument, Fee Amount	(4,161,000)
Debt Instrument, Net Carrying Amount	88,317,000
Convertible Subordinated Debt | Convertible Senior Subordinated Debentures at 4.125% February 2027
Debt Instrument [Line Items]
Debt Instrument, Face Amount			$ 135,000,000
Long-term debt	0	13,039,000
Debt Instrument, Unamortized Discount		(311,000)
Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Long-term debt	$ 32,052,000	$ 33,151,000