Components of Long Term Debt (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Principal amount of convertible notes outstanding	$ 429,349	$ 450,250
Unamortized discount of liability component	(28,255)	(30,020)
Less: current portion	(3,923)	(3,381)
Long-term debt	397,171	416,849
Term loan credit agreement
Debt Instrument [Line Items]
Principal amount of convertible notes outstanding	277,000	297,750
Industrial revenue bond
Debt Instrument [Line Items]
Principal amount of convertible notes outstanding	2,349	2,500
Convertible Senior Notes
Debt Instrument [Line Items]
Principal amount of convertible notes outstanding	150,000	150,000
Unamortized discount of liability component	(21,259)	(23,082)
Less: current portion	0	0
Long-term debt	$ 128,741	$ 126,918