Employee Benefit Plans (Pension Benefit Plan) - Schedule of Cash Equivalents and Investments Held at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 32,263	$ 28,016	$ 24,159
Pension Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	32,263	28,016
Pension Benefit Plan [Member] \| Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,935	691
Pension Benefit Plan [Member] \| Available-For-Sale Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	30,328	27,325
Pension Benefit Plan [Member] \| Government Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,971	6,645
Pension Benefit Plan [Member] \| Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,746	5,514
Pension Benefit Plan [Member] \| Emerging Markets Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	307	531
Pension Benefit Plan [Member] \| Global Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11,638	11,071
Pension Benefit Plan [Member] \| Emerging Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,848	956
Pension Benefit Plan [Member] \| Balanced Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,515	863
Pension Benefit Plan [Member] \| Large Cap Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	198	312
Pension Benefit Plan [Member] \| Global Real Estate Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	799	902
Pension Benefit Plan [Member] \| Managed Futures Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	306	531
Pension Benefit Plan [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	32,263	28,016
Pension Benefit Plan [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,935	691
Pension Benefit Plan [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Available-For-Sale Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	30,328	27,325
Pension Benefit Plan [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Government Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,971	6,645
Pension Benefit Plan [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,746	5,514
Pension Benefit Plan [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Emerging Markets Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	307	531
Pension Benefit Plan [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Global Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11,638	11,071
Pension Benefit Plan [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Emerging Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,848	956
Pension Benefit Plan [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Balanced Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,515	863
Pension Benefit Plan [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Large Cap Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	198	312
Pension Benefit Plan [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Global Real Estate Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	799	902
Pension Benefit Plan [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Managed Futures Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 306	$ 531