Debt (Schedule of Carrying Values of Long-Term Debt) (Details)			9 Months Ended			9 Months Ended		9 Months Ended				9 Months Ended				9 Months Ended		9 Months Ended				9 Months Ended
	Sep. 30, 2014 USD ($)	Dec. 31, 2013 USD ($)	Sep. 30, 2014 Credit Facility [Member]	Sep. 30, 2014 Credit Facility [Member] Revolving Loans [Member] USD ($)	Dec. 31, 2013 Credit Facility [Member] Revolving Loans [Member] USD ($)	Sep. 30, 2014 Senior Notes [Member] Unsecured Debt [Member] 4.875% Senior Notes [Member] USD ($)	Dec. 31, 2013 Senior Notes [Member] Unsecured Debt [Member] 4.875% Senior Notes [Member] USD ($)	Sep. 30, 2014 Convertible Debt [Member] Unsecured Debt [Member] 2011 4.0% Notes [Member]	Sep. 30, 2014 Convertible Debt [Member] Unsecured Debt [Member] 2009 4.0% Notes [Member]	Sep. 30, 2014 Convertible Debt [Member] Unsecured Debt [Member] 2011 4.0% Notes [Member] USD ($)	Dec. 31, 2013 Convertible Debt [Member] Unsecured Debt [Member] 2011 4.0% Notes [Member] USD ($)	Sep. 30, 2014 Convertible Debt [Member] Unsecured Debt [Member] 2011 4.25% Notes [Member] USD ($)	Dec. 31, 2013 Convertible Debt [Member] Unsecured Debt [Member] 2011 4.25% Notes [Member] USD ($)	Sep. 30, 2014 Convertible Debt [Member] Unsecured Debt [Member] 2009 4.0% Notes [Member] USD ($)	Dec. 31, 2013 Convertible Debt [Member] Unsecured Debt [Member] 2009 4.0% Notes [Member] USD ($)	Sep. 30, 2014 Convertible Debt [Member] Unsecured Debt [Member] 2009 4.25% Notes [Member] USD ($)	Dec. 31, 2013 Convertible Debt [Member] Unsecured Debt [Member] 2009 4.25% Notes [Member] USD ($)	Sep. 30, 2014 Other Credit Facilities [Member]	Sep. 30, 2014 Other Credit Facilities [Member] Revolving Loans [Member] USD ($)	Sep. 30, 2014 Other Credit Facilities [Member] Revolving Loans [Member] CAD	Dec. 31, 2013 Other Credit Facilities [Member] Revolving Loans [Member] USD ($)	Sep. 30, 2014 Capital Lease Obligations [Member]	Sep. 30, 2014 Notes Payable [Member] Equipment [Member] USD ($)	Dec. 31, 2013 Notes Payable [Member] Equipment [Member] USD ($)
Debt Instrument [Line Items]
Line of credit facility, maturity date			Oct. 29, 2018															Mar. 03, 2015
Debt instrument, maturity date						Mar. 15, 2023		Jun. 15, 2014	Jun. 15, 2014			Dec. 15, 2014				Dec. 15, 2014
Capital lease obligations, expiration date, range, end																						Jun. 13, 2021
Notes payable, maturity date, range, end																							Sep. 01, 2018
Carrying value of debt				$ 449,500,000	$ 53,000,000	$ 400,000,000	$ 400,000,000			$ 0	$ 103,800,000	$ 96,400,000	$ 94,500,000	$ 0	$ 9,600,000	$ 3,000,000	$ 3,000,000		$ 4,800,000	5,400,000	$ 0		$ 42,800,000	$ 26,900,000
Capital lease obligations	163,600,000	126,000,000
Total debt	1,160,100,000	816,800,000
Less current maturities	(71,798,000)	(51,376,000)
Long-term debt	$ 1,088,289,000	$ 765,425,000