Long-Term Debt (Details 1) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
2.25% Convertible Senior Notes due 2036 [Member]
Carrying value of Notes related discount and equity component
Carrying amount of equity component	$ 65,270	$ 65,270
Allocated underwriter fees, net of taxes	(1,475)	(1,475)
Allocated debt issuance cost, net of taxes	(58)	(58)
Total net equity component	63,737	63,737
Deferred income tax component	9,463	10,846
Principal amount of Notes	182,753	182,753
Unamortized discount	(25,483)	(29,244)
Unamortized underwriter fees	(998)	(1,146)
Secured Long-term Debt, Noncurrent	156,272	152,363
Unamortized debt issuance cost	40	45
3.00% Convertible Senior Notes due 2020 [Member]
Carrying value of Notes related discount and equity component
Carrying amount of equity component	25,359	25,359
Allocated underwriter fees, net of taxes	(760)	(760)
Allocated debt issuance cost, net of taxes	(112)	(112)
Total net equity component	24,487	24,487
Deferred income tax component	11,248	11,844
Principal amount of Notes	115,000	115,000
Unamortized discount	(30,835)	(32,505)
Unamortized underwriter fees	(1,697)	(1,789)
Secured Long-term Debt, Noncurrent	82,468	80,706
Unamortized debt issuance cost	$ 250	$ 264