Long-Term Debt (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Long-term debt	$ 1,600,000	$ 1,500,000
Less: current portion		(400,000)
Total long-term debt	1,600,000	1,100,000
Medium-term notes
Debt Instrument [Line Items]
Long-term debt		50,000
2008 Senior Notes
Debt Instrument [Line Items]
Long-term debt		350,000
2010 Senior Notes
Debt Instrument [Line Items]
Long-term debt	500,000	500,000
2011 Senior Notes
Debt Instrument [Line Items]
Long-term debt	600,000	600,000
2013 Senior Notes
Debt Instrument [Line Items]
Long-term debt	$ 500,000