Debt (Schedule of Long Term Debt Instruments) (Detail) (USD $)			12 Months Ended			12 Months Ended			12 Months Ended			12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended			12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Line of Credit [Member] 2013 Credit Facility [Member]	Dec. 31, 2013 Line of Credit [Member] 2013 Credit Facility [Member] Revolving Credit Facility [Member]	Dec. 31, 2012 Line of Credit [Member] 2011 Credit Facility [Member] Revolving Credit Facility [Member]	Dec. 31, 2013 Maximum [Member] Capital Lease Obligations [Member]	Dec. 31, 2013 Machinery and Equipment [Member] Equipment Notes Payable [Member]	Dec. 31, 2012 Machinery and Equipment [Member] Equipment Notes Payable [Member]	Dec. 31, 2013 Machinery and Equipment [Member] Maximum [Member] Equipment Notes Payable [Member]	Dec. 31, 2013 Unsecured Debt [Member] Senior Notes [Member] 4.875% Senior Notes [Member]	Dec. 31, 2012 Unsecured Debt [Member] Senior Notes [Member] 4.875% Senior Notes [Member]	Dec. 31, 2013 Unsecured Debt [Member] Senior Notes [Member] 7.625% Senior Notes [Member]	Dec. 31, 2012 Unsecured Debt [Member] Senior Notes [Member] 7.625% Senior Notes [Member]	Dec. 31, 2013 Unsecured Debt [Member] Convertible Debt [Member] 2011 4.0% Notes [Member]	Dec. 31, 2012 Unsecured Debt [Member] Convertible Debt [Member] 2011 4.0% Notes [Member]	Dec. 31, 2013 Unsecured Debt [Member] Convertible Debt [Member] 2011 4.25% Notes [Member]	Dec. 31, 2012 Unsecured Debt [Member] Convertible Debt [Member] 2011 4.25% Notes [Member]	Dec. 31, 2013 Unsecured Debt [Member] Convertible Debt [Member] 2009 4.0% Notes [Member]	Dec. 31, 2012 Unsecured Debt [Member] Convertible Debt [Member] 2009 4.0% Notes [Member]	Jun. 30, 2009 Unsecured Debt [Member] Convertible Debt [Member] 2009 4.0% Notes [Member]	Dec. 31, 2013 Unsecured Debt [Member] Convertible Debt [Member] 2009 4.25% Notes [Member]	Dec. 31, 2012 Unsecured Debt [Member] Convertible Debt [Member] 2009 4.25% Notes [Member]	Nov. 30, 2009 Unsecured Debt [Member] Convertible Debt [Member] 2009 4.25% Notes [Member]
Debt Instrument [Line Items]
Line of credit facility, expiration date			Oct. 29, 2018
Debt instrument, maturity date									May 01, 2018	Mar. 15, 2023		Feb. 01, 2017		Jun. 15, 2014		Dec. 15, 2014		Jun. 15, 2014			Dec. 15, 2014
Lease expiration date						Mar. 30, 2020
Credit facility, amount outstanding				$ 53,000,000	$ 134,000,000
Debt instrument, principal amount										400,000,000			150,000,000	105,300,000		97,000,000				115,000,000			100,000,000
Carrying value of debt							26,900,000	30,200,000			0	0	150,000,000.0	103,800,000	100,900,000	94,500,000	92,100,000	9,600,000	9,700,000		3,000,000	3,000,000
Capital lease obligations	126,000,000	79,000,000
Total debt	816,800,000	598,900,000
Less current maturities	(51,376,000)	(52,596,000)
Long-term debt	$ 765,425,000	$ 546,323,000