Summary of Long-Term Debt (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 10.375% Senior Unsecured Notes due 2016	Dec. 31, 2012 10.375% Senior Unsecured Notes due 2016	Dec. 31, 2009 10.375% Senior Unsecured Notes due 2016	Dec. 31, 2013 7.25% Senior Unsecured Notes due 2019	Dec. 31, 2012 7.25% Senior Unsecured Notes due 2019	Feb. 29, 2012 7.25% Senior Unsecured Notes due 2019	Dec. 31, 2013 Senior Notes Due 2020 [Member]	Dec. 31, 2012 Senior Notes Due 2020 [Member]
Debt Instrument [Line Items]
Revolving credit facility	$ 206,000	$ 0
Senior notes			0	294,759		300,000	300,000		775,000	0
Long-term debt	1,281,000	594,759
Principal amount			$ 0	$ 300,000
Annual interest rate					10.375%	7.25%		7.25%	8.50%