Debt - Schedule of the Company's Debt (Parenthetical) (Detail)			3 Months Ended	6 Months Ended
	Mar. 20, 2014	Mar. 13, 2012	Mar. 31, 2015	Jun. 30, 2015	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	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