Debt (Long Term Debt Instruments) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Capital lease obligations	$ 79,000,000
Capital lease obligations	82,200,000
Total debt	598,900,000	494,800,000
Less current maturities	(52,596,000)	(34,050,000)
Long-term debt	546,323,000	460,690,000
Line of Credit [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, expiration date	Aug. 22, 2016
Credit facility, amount outstanding	134,000,000	60,000,000
7.625% Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	Feb. 01, 2017
Carrying value of debt	150,000,000	150,000,000
Convertible Debt [Member] | New 4.0% Notes [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	Jun. 15, 2014
Carrying value of debt	100,900,000	98,200,000
Convertible Debt [Member] | New 4.25% Notes [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	Dec. 15, 2014
Carrying value of debt	92,100,000	89,900,000
Convertible Debt [Member] | Original 4.0% Notes [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	Jun. 15, 2014
Carrying value of debt	9,700,000	9,700,000
Convertible Debt [Member] | Original 4.25% Notes [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	Dec. 15, 2014
Carrying value of debt	3,000,000	3,000,000
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Lease expiration date	Jun. 30, 2019
Capital lease obligations	79,000,000	40,600,000
Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	May 31, 2018
Carrying value of debt	$ 30,200,000	$ 43,400,000