Schedule of Market Values of Pension Plan Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 120,287	$ 104,591	$ 118,667
Equity Securities U.S. Large Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9,867	7,711
Equity Securities U.S. Mid Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,054	2,309
Equity Securities U.S. Small Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,160	2,094
Equity Securities International Developed
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7,317	5,710
Equity Securities Emerging Markets
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,957	4,137
Fixed Income Securities Core Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	25,390	24,617
Fixed Income Securities Long Duration Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	63,515	55,318
Real Estate REIT Fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,372	2,037
Cash Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 655	$ 658