Investments Held in Rabbi Trust - Components of Investment Income (Losses), Included in Other Income (Expense), Net in Accompanying Consolidated Statements of Operations (Detail) - Other Income (Expense), Net [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized gains (losses) from sale of trading securities	$ 61	$ 5
Dividend and interest income	29	25
Net unrealized holding gains (losses)	1,090	(55)
Net investment income (losses)	$ 1,180	$ (25)