Credit Agreement - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013
Line of Credit Facility [Line Items]
Unsecured revolving credit facility	$ 750
Unsecured revolving credit facility, additional commitment	$ 250
Before Amendment
Line of Credit Facility [Line Items]
Unsecured revolving credit facility expiration date	Oct. 18, 2013
After Amendment
Line of Credit Facility [Line Items]
Unsecured revolving credit facility expiration date	Oct. 09, 2014
Eurodollar | Minimum
Line of Credit Facility [Line Items]
Unsecured revolving credit facility, applicable margin on borrowing rate	1.00%
Eurodollar | Maximum
Line of Credit Facility [Line Items]
Unsecured revolving credit facility, applicable margin on borrowing rate	1.25%
Base Rate | Minimum
Line of Credit Facility [Line Items]
Unsecured revolving credit facility, applicable margin on borrowing rate	0.00%
Base Rate | Maximum
Line of Credit Facility [Line Items]
Unsecured revolving credit facility, applicable margin on borrowing rate	0.25%