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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized gains (losses) from sale of trading securities	$ 309	$ 12	$ 734	$ 62
Dividend and interest income	41	48	73	81
Net unrealized holding gains (losses)	773	1,756	841	(384)
Net investment income (losses)	$ 1,123	$ 1,816	$ 1,648	$ (241)