Employee Benefits - Fair Value of Plan Assets and Major Categories (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Percentage	100.00%	100.00%
Total, fair value of plan assets	$ 51,660	$ 44,437
Estimated Fair Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Percentage	49.10%	47.30%
Total, fair value of plan assets	$ 25,386	$ 21,039
Fair Value Measurements, Level 1 Inputs [Member]
Defined Benefit Plan Disclosure [Line Items]
Total, fair value of plan assets	25,386	21,039
Fair Value Measurements, Level 1 Inputs [Member] | Estimated Fair Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Total, fair value of plan assets	$ 25,386	$ 21,039
Fair Value Measured at Net Asset Value Per Share [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Percentage	50.90%	52.70%
Total, fair value of plan assets	$ 26,274	$ 23,398
Collective Funds [Member] | Estimated Fair Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Percentage	8.30%	5.60%
Total, fair value of plan assets	$ 4,289	$ 2,504
Collective Funds [Member] | Fair Value Measurements, Level 1 Inputs [Member] | Estimated Fair Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Total, fair value of plan assets	$ 4,289	$ 2,504
Equity Securities [Member] | Estimated Fair Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Percentage	9.70%	10.90%
Total, fair value of plan assets	$ 5,016	$ 4,863
Equity Securities [Member] | Fair Value Measurements, Level 1 Inputs [Member] | Estimated Fair Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Total, fair value of plan assets	$ 5,016	$ 4,863
Diversified [Member] | Estimated Fair Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Percentage	31.10%	30.70%
Total, fair value of plan assets	$ 16,081	$ 13,612
Diversified [Member] | Fair Value Measurements, Level 1 Inputs [Member] | Estimated Fair Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Total, fair value of plan assets	$ 16,081	$ 13,612
Short-Term Investments [Member] | Estimated Fair Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Percentage		0.10%
Total, fair value of plan assets		$ 60
Short-Term Investments [Member] | Fair Value Measurements, Level 1 Inputs [Member] | Estimated Fair Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Total, fair value of plan assets		$ 60