Schedule of Market Values of Pension Plan Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 104,591	$ 118,667	$ 109,677
Equity Securities U.S. Large Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7,711	9,393
Equity Securities U.S. Mid Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,309	2,937
Equity Securities U.S. Small Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,094	3,005
Equity Securities International Developed
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,710	7,213
Equity Securities Emerging Markets
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,137	4,792
Fixed Income Securities Core Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	24,617	25,915
Fixed Income Securities Long Duration Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	55,318	62,522
Real Estate REIT Fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,037	2,370
Cash Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 658	$ 520