Debt (Details) (USD $)	3 Months Ended		6 Months Ended		1 Months Ended					1 Months Ended	6 Months Ended		1 Months Ended			1 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Aug. 31, 2012 Subsequent event	Jan. 31, 2012 Term Loan maturing in 2016	Jun. 30, 2012 Term Loan maturing in 2016	Jun. 30, 2012 Term Loan maturing in 2016 Minimum	Jun. 30, 2012 Term Loan maturing in 2016 Maximum	Jan. 31, 2012 7 3/8% senior notes, due 2012	Jun. 30, 2012 7 3/8% senior notes, due 2012	Dec. 31, 2011 7 3/8% senior notes, due 2012	Aug. 31, 2012 7 3/8% senior notes, due 2012 Subsequent event	Jun. 30, 2012 7 3/4% senior notes, due 2016	Dec. 31, 2011 7 3/4% senior notes, due 2016	Aug. 31, 2012 7 3/4% senior notes, due 2016 Subsequent event
Long Term Debt
Additional borrowings						$ 275,000,000
Quarterly principal payment as a percent of the original principal amount								1.25%	3.75%
Unpaid principal balance payment							158,000,000
Note stated interest rate (as a percent)										7.375%		7.375%		7.75%	7.75%
Aggregate principal amount of debt securities that the Company plans to sell					750,000,000
Repayments of Debt	21,896,000	491,000	305,344,000	7,816,000						279,700,000
Prospective debt repayment													210,000,000			500,000,000
Senior notes												261,250,000		500,000,000	500,000,000
Aggregate principal amount outstanding											420,300,000
Expenses recorded related to tender premium, unamortized debt issuance cost write-off, and tender expenses											$ 13,900,000