Debt - Schedule of the Company's Debt (Parenthetical) (Detail)	3 Months Ended	0 Months Ended
	Mar. 31, 2015	Mar. 20, 2014	Mar. 13, 2012	Dec. 31, 2014
5.50% Senior Notes Due May 15, 2015
Debt Instrument [Line Items]
Interest rate	5.50%
Maturity date	May 15, 2015
8.60% Senior Notes Due August 15, 2016
Debt Instrument [Line Items]
Interest rate	8.60%
Maturity date	Aug. 15, 2016
6.125% Senior Notes Due January 15, 2017
Debt Instrument [Line Items]
Interest rate	6.125%
Maturity date	Jan. 15, 2017
7.25% Senior Notes Due May 15, 2018
Debt Instrument [Line Items]
Interest rate	7.25%	7.25%
Maturity date	May 15, 2018	May 15, 2018
11.25% Senior Notes Due February 1, 2019
Debt Instrument [Line Items]
Interest rate	11.25%
Maturity date	Feb. 01, 2019
Effective interest rate				12.75%
8.25% Senior Notes Due March 15, 2019
Debt Instrument [Line Items]
Interest rate	8.25%	8.25%	8.25%
Maturity date	Mar. 15, 2019	Mar. 15, 2019	Mar. 15, 2019
7.625% Senior Notes Due June 15, 2020
Debt Instrument [Line Items]
Interest rate	7.625%	7.625%
Maturity date	Jun. 15, 2020	Jun. 15, 2020
7.875% Senior Notes Due March 15, 2021
Debt Instrument [Line Items]
Interest rate	7.875%
Maturity date	Mar. 15, 2021
8.875% Debentures Due April 15, 2021
Debt Instrument [Line Items]
Interest rate	8.875%
Maturity date	Apr. 15, 2021
7.00% Senior Notes Due February 15, 2022
Debt Instrument [Line Items]
Interest rate	7.00%
Maturity date	Feb. 15, 2022
6.50% Senior Notes Due November 15, 2023
Debt Instrument [Line Items]
Interest rate	6.50%
Maturity date	Nov. 15, 2023
6.00% Senior Notes Due due April 1, 2024
Debt Instrument [Line Items]
Interest rate	6.00%
Maturity date	Apr. 01, 2024
6.625% Debentures Due April 15, 2029
Debt Instrument [Line Items]
Interest rate	6.625%
Maturity date	Apr. 15, 2029
8.820% Debentures Due April 15, 2031
Debt Instrument [Line Items]
Interest rate	8.82%
Maturity date	Apr. 15, 2031