Long-Term Debt (Schedule of Long-Term Debt) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Long-term Debt	$ 749,150,000	$ 1,135,110,000
Senior Notes Series A Due February Twenty Seven Two Thousand Twenty [Member]
Debt Instrument [Line Items]
Credit facility, amount outstanding	150,000,000	82,500,000
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	350,000,000	192,500,000
Credit facility, expiration date	Feb. 27, 2023
Long term debt, face amount	350,000,000
Credit Line Due June Twenty Nine Two Thousand Fourteen [Member]
Debt Instrument [Line Items]
Credit facility, amount outstanding	0	7,110,000
Credit facility, expiration date	Jun. 29, 2014
Long term debt, face amount	10,000,000
Term Loan Due July 1, 2016 [Member]
Debt Instrument [Line Items]
Credit facility, amount outstanding	208,000,000	468,000,000
Credit facility, expiration date	Jul. 01, 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	41,150,000	185,000,000
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	3,930,000
Senior Notes [Member]
Debt Instrument [Line Items]
Senior notes due February 28, 2013	$ 0	$ 200,000,000
Credit facility, expiration date	Feb. 28, 2013