Debt (Credit Agreement) (Details) (USD $)	3 Months Ended				3 Months Ended		3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Apr. 30, 2012	Mar. 31, 2012 Revolving Credit Facility [Member]	Mar. 31, 2012 Term Loan [Member]	Dec. 31, 2011 Term Loan [Member]	Mar. 31, 2012 Minimum [Member]	Mar. 31, 2012 Maximum [Member]
Line of Credit Facility [Line Items]
Line of credity facility, principal amount				$ 500,000,000	$ 500,000,000
Eurodollar Rate margin, basis points					275		187.5	237.5
Base Rate margin, basis points					175		87.5	137.5
Line of credit facility, per annum commitment fee							0.375%	0.50%
Borrowings under the Revolving Credit Facility	200,000,000	175,000,000
Line of credit facility, remaining borrowing capacity			116,000,000	300,000,000
Revolving credit facility under senior credit agreement	100,000,000
Line of credit facility additional borrowed	284,000,000
Debt instrument, maturity date					Jun. 30, 2018
Base Rate floor					2.00%
Eurodollar Rate floor					1.00%
Debt instrument, principal balance					496,300,000	497,500,000
Repayments of long-term debt, quarterly					1,250,000
Prepayment fee, percentage					1.00%
Percentage of par value price for issuance of term loan					99.75%
Repayments of debt	$ 1,250,000				$ 1,250,000