Interest Expense (Income) - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Dec. 31, 2017	Jun. 30, 2018
Interest Expense [Line Items]
Long term debt, repaid		$ 500,000
Notes, 5.75%, Due 2017 [Member]
Interest Expense [Line Items]
Long term debt, repaid	$ 600,000
Debt instrument interest rate		5.75%

The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3291-108585

Name:	us-gaap_RepaymentsOfLongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration