Debt - Fair Values of Senior Notes and Outstanding Debt under Credit Facility (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Total senior notes	$ 483,250	$ 511,000
5 1/2% Senior Notes Due 2021 [Member]
Debt Instrument [Line Items]
Total senior notes	191,500	202,000
6 3/8% Senior Notes Due 2023 [Member]
Debt Instrument [Line Items]
Total senior notes	291,750	309,000
Bank Credit Facility [Member]
Debt Instrument [Line Items]
Total senior notes	$ 1,317,990	$ 1,426,126