Debt (6.375% Senior Notes Due 2020) (Details) (USD $)	0 Months Ended			12 Months Ended		0 Months Ended	12 Months Ended		12 Months Ended
	Mar. 09, 2012 Senior Notes 6.375% Due 2022	Dec. 31, 2012 Senior Notes 6.375% Due 2022	Dec. 31, 2011 Senior Notes 6.375% Due 2022	Dec. 31, 2012 Senior Notes 10.25 Percent Due 2014	Dec. 31, 2011 Senior Notes 10.25 Percent Due 2014	Nov. 01, 2010 Senior Notes 6.75 Percent Due 2020	Dec. 31, 2012 Senior Notes 6.75 Percent Due 2020	Dec. 31, 2011 Senior Notes 6.75 Percent Due 2020	Dec. 31, 2012 March 9, 2012 Through March 14, 2015 Senior Notes 6.375% Due 2022	Dec. 31, 2012 March 15, 2017 through March 14, 2018 Senior Notes 6.375% Due 2022	Dec. 31, 2012 March 15, 2018 through March 14, 2019 Senior Notes 6.375% Due 2022	Dec. 31, 2012 March 15, 2019 through March 14, 2020 Senior Notes 6.375% Due 2022	Dec. 31, 2012 March 15, 2020 and thereafter Senior Notes 6.375% Due 2022	Dec. 31, 2012 March 9, 2012 through March 14, 2017 Senior Notes 6.375% Due 2022	Dec. 31, 2012 Minimum redemption notice at stipulated date and rate Senior Notes 6.375% Due 2022	Dec. 31, 2012 Maximum redemption notice at stipulated date and rate Senior Notes 6.375% Due 2022
Debt Instrument
Interest rate on debt instrument (as a percent)		6.375%		10.25%			6.75%
Senior Notes Redemption Price, Notice Period Range in Days															30 days	60 days
Net proceeds from Issuance long-term debt	$ 589,500,000					$ 294,000,000
Senior Notes	$ 600,000,000	$ 600,000,000	$ 0	$ 202,917,000	$ 348,692,000	$ 300,000,000	$ 300,000,000	$ 300,000,000
Debt Instrument Redemption Percentage, Maximum									35.00%
Senior notes redemption price percentage of principal									106.375%	103.188%	102.125%	101.063%	100.00%
Debt Instrument redemption price percentage of principal amount plus make whole premium and accrued and unpaid interest				100.00%			100.00%							100.00%