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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized gains (losses) from sale of trading securities	$ 5	$ 27	$ 66	$ 32
Dividend and interest income	53	43	82	68
Net unrealized holding gains (losses)	368	72	1,458	17
Net investment income (losses)	$ 426	$ 142	$ 1,606	$ 117