Debt - Fair Values of Senior Notes and Outstanding Debt under Credit Facility (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Total senior notes	$ 200,750	$ 200,500
5 1/2% Senior Notes Due 2021 [Member]
Debt Instrument [Line Items]
Total senior notes	200,750	200,500
Bank Credit Facility [Member]
Debt Instrument [Line Items]
Total senior notes	$ 1,013,340	$ 992,775

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

No definition available.

Name:	us-gaap_LongTermDebtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant