Investments Held in Rabbi Trust - Investments Held in Rabbi Trust, Classified as Trading (Detail) - Mutual Funds [Member] - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule of Trading Securities and Other Trading Assets [Line Items]
Mutual funds, Cost	$ 9,368	$ 8,864
Other Current Assets [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Mutual funds, Fair Value	$ 13,075	$ 11,442

Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.4)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Name:	us-gaap_TradingSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant