Benefit Plans - Change in Projected Benefit Obligation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in projected benefit obligation:
Projected benefit obligation at beginning of year	$ 157,364	$ 170,566
Interest cost	6,113	5,542	$ 5,713
Actuarial loss (gain)	20,001	(11,540)
Benefits paid	(8,073)	(7,204)
Projected benefit obligation at end of year	175,405	157,364	170,566
Change in fair value of plan assets:
Fair value of plan assets at beginning of year	210,508	222,124
Actual return (loss) on plan assets	32,835	(5,545)
Employer contributions	1,351	1,133
Benefits paid	(8,073)	(7,204)
Fair value of plan assets at end of year	236,621	210,508	$ 222,124
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Asset recognized	61,216	53,144
Accumulated benefit obligation	175,405	157,364
Accrued interest receivable	$ 641	$ 660