Schedule of Debt Outstanding (Parenthetical) (Detail)	6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Revolving Credit Facility
Debt Instrument [Line Items]
Revolving Credit Facility maturity date	Dec. 31, 2017
Weighted average rate	1.70%	1.70%
Senior Notes interest payable dates	interest payable periodically at variable interest rates.
Senior Notes 4.625% Due 2023
Debt Instrument [Line Items]
Interest rate stated percentage of Senior Notes	4.625%
Note maturity date	May 31, 2023
Senior Notes interest payable dates	interest payable semi-annually in May and November at 4.625%.
Senior Notes 4.125% Due 2020
Debt Instrument [Line Items]
Interest rate stated percentage of Senior Notes	4.125%
Note maturity date	Apr. 30, 2020
Senior Notes interest payable dates	interest payable semi-annually in April and October at 4.125%.
Senior Notes 7.75% Due 2017
Debt Instrument [Line Items]
Interest rate stated percentage of Senior Notes	7.75%
Note maturity date	Jun. 30, 2017
Senior Notes interest payable dates	interest payable semi-annually in June and December at 7.75%.