Schedule of Debt Outstanding (Parenthetical) (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Unamortized debt issuance costs	$ 11,923,000	$ 9,545,000
Senior Notes 4.625% Due 2023
Debt Instrument [Line Items]
Stated interest rate	4.625%
Debt maturity date	May 01, 2023
Interest payable dates	interest payable semi-annually in May and November at 4.625%.
Unamortized debt issuance costs	$ 4,500,000	5,200,000
Senior Notes 4.125% Due 2020
Debt Instrument [Line Items]
Stated interest rate	4.125%
Debt maturity date	Apr. 01, 2020
Interest payable dates	interest payable semi-annually in April and October at 4.125%.
Unamortized debt issuance costs	$ 3,500,000	4,300,000
Senior Notes 5.0% Due 2022
Debt Instrument [Line Items]
Stated interest rate	5.00%
Debt maturity date	Oct. 15, 2022
Interest payable dates	interest payable semi-annually in April and October at 5.0%.
Unamortized debt issuance costs	$ 3,300,000
Revolving Credit Facility | $900.0 Million Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility maximum borrowing capacity	$ 900,000,000	$ 900,000,000
Revolving Credit Facility maturity date	Jul. 31, 2020
Weighted average rate	1.90%	1.90%
Interest payable dates	interest payable periodically at variable interest rates.
Term Loan Due in July 2020
Debt Instrument [Line Items]
Debt interest rate	2.00%
Debt maturity date	Jul. 31, 2020
Interest payable dates	interest payable periodically at variable interest rates.
Unamortized debt issuance costs	$ 600,000