Long-Term Debt - Outstanding Long-Term Debt (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2012
9.57% bond, due May 1, 2018 [Member]
Debt Instrument [Line Items]
Long-term debt, interest percentage	9.57%
Debt instrument, maturity date	May 01, 2018
10.03% bond, due May 1, 2018 [Member]
Debt Instrument [Line Items]
Long-term debt, interest percentage	10.03%
Debt instrument, maturity date	May 01, 2018
9.08% bond, due June 1, 2022 [Member]
Debt Instrument [Line Items]
Long-term debt, interest percentage	9.08%
Debt instrument, maturity date	Jun. 01, 2022
7.83% note, due January 1, 2015 [Member]
Debt Instrument [Line Items]
Long-term debt, interest percentage	7.83%
Debt instrument, maturity date	Jan. 01, 2015
6.64% note, due October 31, 2017 [Member]
Debt Instrument [Line Items]
Long-term debt, interest percentage	6.64%
Debt instrument, maturity date	Oct. 31, 2017
5.50% note, due October 12, 2020 [Member]
Debt Instrument [Line Items]
Long-term debt, interest percentage	5.50%
Debt instrument, maturity date	Oct. 12, 2020
5.93% note, due October 31, 2023 [Member]
Debt Instrument [Line Items]
Long-term debt, interest percentage	5.93%
Debt instrument, maturity date	Oct. 31, 2023
5.68% note, due June 30, 2026 [Member]
Debt Instrument [Line Items]
Long-term debt, interest percentage	5.68%
Debt instrument, maturity date	Jun. 30, 2026
8.25% due March 1, 2014 [Member]
Debt Instrument [Line Items]
Long-term debt, interest percentage	8.25%
Debt instrument, maturity date	Mar. 01, 2014