Debt (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012 7.50% notes due 2021	Jun. 30, 2011 7.50% notes due 2021	Dec. 31, 2012 5.60% notes due 2012	Dec. 31, 2011 5.60% notes due 2012	Jun. 30, 2011 5.60% notes due 2012	Dec. 31, 2007 5.60% notes due 2012	Dec. 31, 2012 6.30% notes due 2013	Dec. 31, 2011 6.30% notes due 2013	Jun. 30, 2011 6.30% notes due 2013	Jun. 30, 2008 6.30% notes due 2013	Dec. 31, 2012 10.125% notes due 2015	Dec. 31, 2011 10.125% notes due 2015	Feb. 28, 2009 10.125% notes due 2015	Dec. 31, 2012 6.50% notes due 2016	Dec. 31, 2011 6.50% notes due 2016	Jun. 30, 2011 6.50% notes due 2016	Dec. 31, 2012 6.40% notes due 2017	Dec. 31, 2011 6.40% notes due 2017	Dec. 31, 2007 6.40% notes due 2017	Dec. 31, 2012 7.00% notes due 2018	Dec. 31, 2011 7.00% notes due 2018	Jun. 30, 2008 7.00% notes due 2018	Dec. 31, 2012 10.375% notes due 2018	Dec. 31, 2011 10.375% notes due 2018	Feb. 28, 2009 10.375% notes due 2018	Dec. 31, 2012 7.15% notes due 2037	Dec. 31, 2011 7.15% notes due 2037	Dec. 31, 2007 7.15% notes due 2037
Debt Instrument [Line Items]
Interest rate	7.50%	7.50%	5.60%		5.60%	5.60%	6.30%		6.30%	6.30%	10.125%		10.125%	6.50%		6.50%	6.40%		6.40%	7.00%		7.00%	10.375%		10.375%	7.15%		7.15%
Maturity year	2021		2012				2013				2015			2016			2017			2018			2018			2037
Decrease in unamortized discounts				$ 49			$ 30	$ 92			$ 265	$ 338					$ 112	$ 131		$ 269	$ 307		$ 1,324	$ 1,474		$ 635	$ 643
Effective interest rate	7.75%						7.48%	7.48%			9.59%	9.59%		6.02%	6.02%		7.41%	7.41%		7.87%	7.87%		10.62%	10.62%		8.05%	8.05%
Increase (decrease) in unamortized deferred gain realized											$ 2,983	$ 3,802		$ 15,060	$ 18,293