Debt - Additional Information (Detail) (USD $)	3 Months Ended			3 Months Ended		3 Months Ended				0 Months Ended	2 Months Ended	3 Months Ended						3 Months Ended		2 Months Ended	3 Months Ended	0 Months Ended	2 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended		0 Months Ended	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Mar. 31, 2014 Senior Notes Six Point Zero Zero Percent Due April One Two Thousand Twenty Four	Mar. 20, 2014 Senior Notes Six Point Zero Zero Percent Due April One Two Thousand Twenty Four	Mar. 20, 2014 Senior Notes Eight Point Two Five Percent Due March Fifteen Two Thousand Nineteen	Mar. 31, 2014 Senior Notes Eight Point Two Five Percent Due March Fifteen Two Thousand Nineteen	Mar. 31, 2012 Senior Notes Eight Point Two Five Percent Due March Fifteen Two Thousand Nineteen	Mar. 13, 2012 Senior Notes Eight Point Two Five Percent Due March Fifteen Two Thousand Nineteen	Mar. 14, 2013 Senior Notes Seven Point Two Five Percent Due May Fifteen Two Thousand Eighteen	Aug. 26, 2013 Senior Notes Seven Point Two Five Percent Due May Fifteen Two Thousand Eighteen	Mar. 20, 2014 Senior Notes Seven Point Two Five Percent Due May Fifteen Two Thousand Eighteen	Mar. 31, 2014 Senior Notes Seven Point Two Five Percent Due May Fifteen Two Thousand Eighteen	Mar. 20, 2014 Senior Notes Seven Point Six Two Five Percent Due June Fifteen Two Thousand Twenty	Mar. 31, 2014 Debt Instruments Extinguished Three	Mar. 31, 2014 Senior Notes Six Point Five Zero Percent Due November Fifteen Two Thousand Twenty Three	Nov. 12, 2013 Senior Notes Six Point Five Zero Percent Due November Fifteen Two Thousand Twenty Three	Mar. 31, 2014 Senior Notes Seven Point Zero Percent Due February Fifteen Two Thousand Twenty Two	Aug. 26, 2013 Senior Notes Seven Point Zero Percent Due February Fifteen Two Thousand Twenty Two	Aug. 26, 2013 Senior Notes Five Point Five Zero Percent Due May Fifteen Two Thousand Fifteen	Mar. 31, 2014 Senior Notes Five Point Five Zero Percent Due May Fifteen Two Thousand Fifteen	Mar. 14, 2013 Senior Notes Six Point One Two Five Percent Due January Fifteen Two Thousand Seventeen	Aug. 26, 2013 Senior Notes Six Point One Two Five Percent Due January Fifteen Two Thousand Seventeen	Mar. 31, 2014 Senior Notes Six Point One Two Five Percent Due January Fifteen Two Thousand Seventeen	Dec. 31, 2013 Debt Instruments Extinguished One	Mar. 31, 2014 Senior Notes Seven Point Eight Seven Five Percent Due March Fifteen Two Thousand Twenty One	Mar. 14, 2013 Senior Notes Seven Point Eight Seven Five Percent Due March Fifteen Two Thousand Twenty One	Mar. 14, 2013 Senior Notes Eight Point Six Zero Percent Due August Fifteen Two Thousand Sixteen	Mar. 31, 2014 Senior Notes Eight Point Six Zero Percent Due August Fifteen Two Thousand Sixteen	Mar. 31, 2013 Debt Instruments Extinguished Two	Mar. 31, 2014 Revolving Credit Facility	Mar. 31, 2013 Revolving Credit Facility
Debt Disclosure [Line Items]
Amount of difference between fair value and book value	$ 400,000,000		$ 343,400,000
Total amount of revolving credit agreement																															1,150,000,000
Weighted average interest rate on borrowings																															2.10%	2.20%
Debt instrument, face amount					400,000,000		239,000,000		450,000,000								350,000,000		400,000,000								450,000,000
Interest rate				6.00%		8.25%	8.25%		8.25%			7.25%	7.25%	7.625%	8.25%	6.50%		7.00%			5.50%			6.125%		7.875%			8.60%
Maturity date				Apr. 01, 2024		Mar. 15, 2019	Mar. 15, 2019	Mar. 15, 2019				May 15, 2018	May 15, 2018	Jun. 15, 2020		Nov. 15, 2023		Feb. 15, 2022			May 15, 2015			Jan. 15, 2017		Mar. 15, 2021			Aug. 15, 2016
Repayment of Debt	552,500,000	386,500,000				211,000,000	211,000,000			50,000,000	200,000,000	100,000,000		50,000,000						100,000,000		173,500,000	100,000,000					130,200,000
Loss on debt extinguishment	(77,100,000)	(35,600,000)													77,100,000										46,300,000					35,600,000
Gain due to termination of related interest rate swaps															2,800,000
Interest income	$ 2,500,000	$ 3,800,000