Debt - Additional Information (Detail) (USD $)	3 Months Ended			3 Months Ended				3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Mar. 31, 2013 Senior Notes Eight Point Twenty Five Percent Due March Fifteen Two Thousand Nineteen	Mar. 31, 2012 Senior Notes Eight Point Twenty Five Percent Due March Fifteen Two Thousand Nineteen	Mar. 31, 2012 Senior Notes Four Point Nine Five Percent Due April One Two Thousand Fourteen	Apr. 09, 2010 Senior Notes Four Point Nine Five Percent Due April One Two Thousand Fourteen	Mar. 31, 2012 Senior Notes Five Point Five Zero Percent Due May Fifteen Two Thousand Fifteen	Mar. 31, 2012 Senior Notes Five Point Six Two Five Percent Due January Fifteen Two Thousand Twelve	Mar. 31, 2013 Senior Notes Seven Point Eight Seven Five Percent Due March Fifteen Two Thousand Twenty One	Mar. 31, 2013 Senior Notes Six Point One Two Five Percent Due January Fifteen Two Thousand Seventeen	Mar. 31, 2013 Senior Notes Eight Point Six Zero Percent Due August Fifteen Two Thousand Sixteen	Mar. 31, 2013 Senior Notes Seven Point Two Five Percent Due May Fifteen Two Thousand Eighteen	Mar. 31, 2013 Revolving Credit Facility
Debt Disclosure [Line Items]
Amount of difference between fair value and book value	$ 217,300,000		$ 3,700,000
Debt instrument, face amount				450,000,000	450,000,000					450,000,000		130,200,000	50,000,000
Interest rate				8.25%	8.25%	4.95%	4.95%	5.50%	5.625%	7.875%	6.125%	8.60%	7.25%
Maturity date				Mar. 15, 2019	Mar. 15, 2019	Apr. 01, 2014		May 15, 2015	Jan. 15, 2012	Mar. 15, 2021	Jan. 15, 2017	Aug. 15, 2016	May 15, 2018
Repayment of debt assumed in acquisition						341,800,000		100,000,000	158,600,000		173,500,000
Pre-tax loss on debt extinguishment	35,600,000	12,100,000
Pre-tax loss on debt extinguishment		23,200,000
Gain due to termination of the related interest rate swaps		11,100,000
Total amount of revolving credit agreement			1,750,000,000											1,150,000,000
Interest income	$ 3,800,000	$ 3,600,000