Estimated Fair Value of Outstanding Debt Balances (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying value of Debt	$ 695,000	$ 698,750
Fair value of Debt	687,074	738,622
Term Loan Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying value of Debt	95,000	98,750
Fair value of Debt	95,000	98,750
Series A Senior Notes, 4.97 Percent
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying value of Debt	300,000	300,000
Fair value of Debt	305,591	329,281
Series B Senior Notes, 4.27 Percent
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying value of Debt	300,000	300,000
Fair value of Debt	$ 286,483	$ 310,591