Long-Term Debt (Schedule of Long-Term Debt) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Senior notes due February 28, 2013	$ 200,000,000	$ 200,000,000
Other long-term debt	0	5,000
Long-term Debt	1,135,110,000	802,005,000
Senior Notes Series A Due February Twenty Seven Two Thousand Twenty [Member]
Debt Instrument [Line Items]
Credit facility, amount outstanding	82,500,000	0
Credit facility, expiration date	Feb. 27, 2020
Long term debt, face amount	150,000,000
Senior Notes Series B Due February Twenty Seven Two Thousand Twenty Three [Member]
Debt Instrument [Line Items]
Credit facility, amount outstanding	192,500,000	0
Credit facility, expiration date	Feb. 27, 2023
Long term debt, face amount	350,000,000
Credit Line Due June Thirty Two Thousand Thirteen [Member]
Debt Instrument [Line Items]
Credit facility, amount outstanding	7,110,000	0
Credit facility, expiration date	Jun. 30, 2013
Long term debt, face amount	10,000,000
Term Loan Due May 31, 2016 [Member]
Debt Instrument [Line Items]
Credit facility, amount outstanding	468,000,000	507,000,000
Credit facility, expiration date	May 31, 2016
Long term debt, face amount	540,000,000
Revolving Credit Facility Due November 9, 2015 [Member]
Debt Instrument [Line Items]
Credit facility, amount outstanding	185,000,000	95,000,000
Credit facility, expiration date	Nov. 09, 2015
Long term debt, face amount	325,000,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, amount outstanding	$ 3,936,000
Senior Notes [Member]
Debt Instrument [Line Items]
Credit facility, expiration date	Feb. 28, 2013