Condensed Consolidating Financial Information (Narrative) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Mar. 31, 2013 Eight Point Six Two Five Percent Senior Notes [Member]	Dec. 31, 2012 Eight Point Six Two Five Percent Senior Notes [Member]	Feb. 28, 2012 Eight Point Six Two Five Percent Senior Notes [Member]	Nov. 30, 2011 Eight Point Six Two Five Percent Senior Notes [Member]	Jun. 30, 2011 Eight Point Six Two Five Percent Senior Notes [Member]	Nov. 30, 2010 Eight Point Six Two Five Percent Senior Notes [Member]	Mar. 31, 2013 Seven Point Five Percent Senior Notes [Member]	Dec. 31, 2012 Seven Point Five Percent Senior Notes [Member]	Sep. 10, 2012 Seven Point Five Percent Senior Notes [Member]
Condensed Consolidating Financial Information [Line Items]
Senior Notes		$ 600,000	$ 600,000	$ 200,000	$ 200,000	$ 400,000	$ 400,000	$ 300,000	$ 300,000
Debt instrument interest rate		8.625%								7.50%
Voting interest of the subsidiary owned by the registrant	100.00%