Employee Benefits - Summary of Defined Pension Plan and Supplemental Insurance Retirement Plan (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net Periodic Benefit Cost [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	$ (307)	$ (421)
Net actuarial loss	(30,891)	(22,724)
Total	(31,198)	(23,145)
Defined Benefit Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service cost		(100)
Net actuarial loss	(7,099)	8,263
Total	(49,434)	(40,509)	$ (47,065)
Defined Benefit Pension Plan [Member] | Net Periodic Benefit Cost [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	(12,920)	(11,854)
Total	(12,920)	(11,854)
Supplemental Insurance/ Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	114	114
Net actuarial loss	(7,537)	3,591
Total	(49,976)	(40,405)	$ (42,579)
Supplemental Insurance/ Retirement Plan [Member] | Net Periodic Benefit Cost [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	(307)	(421)
Net actuarial loss	(17,971)	(10,870)
Total	$ (18,278)	$ (11,291)