Summary of Long-Term Debt (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Revolving credit facility	$ 0	$ 99,000
Total	594,759	697,307
Less: Current portion of long-term debt	0	(4,746)
Long-term debt	594,759	692,561
10.375% Senior Unsecured Notes due 2016
Debt Instrument [Line Items]
Senior notes	294,759	293,561
Principal amount	300,000	300,000
7.25% Senior Unsecured Notes due 2019
Debt Instrument [Line Items]
Senior notes	300,000	300,000
4.50% Convertible Notes due 2012
Debt Instrument [Line Items]
Convertible notes due 2012, net of discount (principal amount of $4,915)	0	4,746
Principal amount	$ 4,915	$ 4,915