Long-Term Debt (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
5.10% Senior Notes
Debt Instrument [Line Items]
Unamortized discount	$ 86	$ 103
Debt instrument, interest rate	5.10%	5.10%
4.50% Senior Notes
Debt Instrument [Line Items]
Unamortized discount	$ 2,657	$ 2,814
Debt instrument, interest rate	4.50%	4.50%