Debt - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended	9 Months Ended		9 Months Ended			9 Months Ended						1 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Sep. 30, 2012 Revolving Credit Facility [Member]	Sep. 30, 2012 Credit Agreement [Member]	Sep. 30, 2012 Credit Agreement [Member] Revolving Credit Facility [Member]	Sep. 30, 2012 8.25% Senior Notes Due March 15, 2019 [Member]	Mar. 13, 2012 8.25% Senior Notes Due March 15, 2019 [Member]	Sep. 30, 2012 4.95% Senior Notes Due April 1, 2014 [Member]	Sep. 30, 2012 5.50% Senior Notes Due May 15, 2015 [Member]	Sep. 30, 2011 5.50% Senior Notes Due May 15, 2015 [Member]	Sep. 30, 2012 5.625% Senior Notes Due January 15, 2012 [Member]	Sep. 30, 2011 Senior Notes Seven Point Twenty Five Percent Due May Fifteen Two Thousand Eighteen [Member]	Jun. 01, 2011 Senior Notes Seven Point Twenty Five Percent Due May Fifteen Two Thousand Eighteen [Member]	Sep. 28, 2011 11.25% Senior Notes Due February 1, 2019 [Member]	Sep. 30, 2011 11.25% Senior Notes Due February 1, 2019 [Member]	Sep. 30, 2011 6.125% Senior Notes Due January 15, 2017 [Member]
Debt Disclosure [Line Items]
Amount of difference between fair value and book value	$ 41,900,000		$ 41,900,000		$ 80,100,000
Credit facility, maximum borrowing capacity						1,150,000,000		1,750,000,000
Revolving credit agreement expiration date						Oct. 15, 2017		Dec. 17, 2013
Allowable annual dividend payment under credit agreement							200,000,000
Debt instrument, face amount									450,000,000	450,000,000						600,000,000
Interest rate									8.25%	8.25%	4.95%	5.50%	5.50%	5.625%	7.25%		11.25%	11.25%	6.125%
Maturity date									Mar. 15, 2019		Apr. 01, 2014	May 15, 2015	May 15, 2015	Jan. 15, 2012	May 15, 2018		Feb. 01, 2019	Feb. 01, 2019	Jan. 15, 2017
Repurchase of debt											341,800,000	100,000,000	100,000,000	158,600,000			11,600,000	216,200,000	100,000,000
Pre-tax loss on debt extinguishment			12,100,000		69,900,000
Pre-tax loss on debt extinguishment			23,200,000
Gain due to termination of the related interest rate swaps			11,100,000
Interest income	$ 3,800,000	$ 2,900,000	$ 11,500,000	$ 9,100,000