Components of Net Periodic Benefit Cost (Narrative) (Detail) - USD ($)			9 Months Ended	12 Months Ended
	Sep. 30, 2021	Jan. 01, 2007	Sep. 30, 2021	Dec. 31, 2002
Retirement Benefits [Abstract]
Service period for employees of coverage age, years (at least)			1 year
Defined benefit plan, percentage vested	100.00%		100.00%
Retiree benefits eliminated if less than service period, years (less than)		10 years		10 years
Defined benefit plan, contributions by employer	$ 0