Employee Benefit Plans (Combined Activity in Corporations Defined Benefit Pension Plans) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Retirement Benefits [Abstract]
Fair value of plan assets at beginning of year	$ 174,173	$ 152,820	$ 168,450
Actual return on plan assets	16,599	29,945	(7,739)
Employer contributions	1,201	1,163	1,077
Benefits paid	(9,885)	(9,755)	(8,968)
Fair value of plan assets at end of year	182,088	174,173	152,820
Benefit obligation at beginning of year	186,641	167,107	182,607
Interest cost	5,010	6,472	5,898
Actuarial (gain) loss	15,827	22,817	(12,430)
Benefits paid	(9,885)	(9,755)	(8,968)
Benefit obligation at end of year	197,593	186,641	167,107
Funded status of the plan at end of year and accrued benefit (liability) recognized	(15,505)	(12,468)	(14,287)
Accumulated benefit obligation at end of year	$ 197,593	$ 186,641	$ 167,107