Estimated Fair Value of Outstanding Debt Balances (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Carrying value of Debt	$ 600,000	$ 855,000
Fair value of Debt	546,728	793,441
Term Loan Facility
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Carrying value of Debt		70,000
Fair value of Debt		70,000
2015 Term Loan
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Carrying value of Debt		185,000
Fair value of Debt		185,000
4.97% Series A Senior Notes, Due October 5th 2020
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Carrying value of Debt	300,000	300,000
Fair value of Debt	283,534	279,635
4.27% Series B Senior Notes, Due June 14th 2022
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Carrying value of Debt	300,000	300,000
Fair value of Debt	$ 263,194	$ 258,806