Schedule I - Condensed Statements of Comprehensive Income (Parent Company Only) (Parenthetical) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Tax benefit on prior service costs, employee benefit plans	$ 17	$ 543
Tax expense (benefit) on actuarial gain (loss), employee benefit plans	(9,219)	131	$ (3,507)
Tax expense, adjustment for items reclassified to earnings, employee benefit plans	(1,167)	(2,335)	(2,220)
Parent Company [Member]
Tax benefit on prior service costs, employee benefit plans	17	543
Tax expense (benefit) on actuarial gain (loss), employee benefit plans	(9,219)	131	(3,507)
Tax expense, adjustment for items reclassified to earnings, employee benefit plans	$ 1,167	$ 2,335	$ 2,220