Long-term Debt - Long-term Debt (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Long-term debt	$ 1,324,383	$ 1,196,908
Bank credit facility [Member]
Debt Instrument [Line Items]
Long-term debt	440,000	600,000
8 3/8% senior notes due 2017 [Member]
Debt Instrument [Line Items]
Long-term debt	300,000	300,000
Discount related to 8 3/8% senior notes due 2017 [Member]
Debt Instrument [Line Items]
Long-term debt	(2,556)	(3,092)
7 3/4% senior notes due 2019 [Member]
Debt Instrument [Line Items]
Long-term debt	300,000	300,000
9 1/2% senior notes due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt	300,000
Discount related to 9 1/2% senior notes due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt	$ (13,061)