Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	$ 56,790
Pension Plans, Defined Benefit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	56,209	$ 56,928
Accrued income	581	608
Total fair value of plan assets	56,790	57,536
Supplemental Executive Retirement Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		8,909
Other pending transactions		(1)
Total fair value of plan assets		8,908
Supplemental Executive Retirement Plan | Measured At Net Asset Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		1,725
Total fair value of plan assets		1,725
Quoted Prices In Active Markets (Level 1) | Pension Plans, Defined Benefit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	6,345	4,629
Accrued income	581	608
Total fair value of plan assets	6,926	5,237
Quoted Prices In Active Markets (Level 1) | Supplemental Executive Retirement Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		6,173
Other pending transactions		(1)
Total fair value of plan assets		6,172
Level 2 | Pension Plans, Defined Benefit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	49,864	52,299
Total fair value of plan assets	49,864	52,299
Level 2 | Supplemental Executive Retirement Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		1,011
Total fair value of plan assets		1,011
US Government Agencies Debt Securities | Pension Plans, Defined Benefit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	4,044	4,238
US Government Agencies Debt Securities | Supplemental Executive Retirement Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		1,692
US Government Agencies Debt Securities | Quoted Prices In Active Markets (Level 1) | Pension Plans, Defined Benefit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	4,044	4,238
US Government Agencies Debt Securities | Quoted Prices In Active Markets (Level 1) | Supplemental Executive Retirement Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		851
US Government Agencies Debt Securities | Level 2 | Supplemental Executive Retirement Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		841
Collateralized mortgage securities | Pension Plans, Defined Benefit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		1,032
Collateralized mortgage securities | Level 2 | Pension Plans, Defined Benefit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		1,032
Corporate Debt Securities | Pension Plans, Defined Benefit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	47,667	49,420
Corporate Debt Securities | Quoted Prices In Active Markets (Level 1) | Pension Plans, Defined Benefit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	684
Corporate Debt Securities | Level 2 | Pension Plans, Defined Benefit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	46,983	49,420
Cash and Cash Equivalents | Pension Plans, Defined Benefit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	1,214	834
Cash and Cash Equivalents | Supplemental Executive Retirement Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		246
Cash and Cash Equivalents | Supplemental Executive Retirement Plan | Measured At Net Asset Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		49
Cash and Cash Equivalents | Quoted Prices In Active Markets (Level 1) | Pension Plans, Defined Benefit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	717	219
Cash and Cash Equivalents | Quoted Prices In Active Markets (Level 1) | Supplemental Executive Retirement Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		27
Cash and Cash Equivalents | Level 2 | Pension Plans, Defined Benefit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	497	615
Cash and Cash Equivalents | Level 2 | Supplemental Executive Retirement Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		170
Other | Pension Plans, Defined Benefit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	2,384	1,404
Other | Quoted Prices In Active Markets (Level 1) | Pension Plans, Defined Benefit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		172
Other | Level 2 | Pension Plans, Defined Benefit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	2,384	1,232
Equity Securities | Pension Plans, Defined Benefit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	900
Equity Securities | Quoted Prices In Active Markets (Level 1) | Pension Plans, Defined Benefit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets	$ 900
Common stock | Supplemental Executive Retirement Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		3,599
Common stock | Quoted Prices In Active Markets (Level 1) | Supplemental Executive Retirement Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		3,599
Foreign Stock | Supplemental Executive Retirement Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		183
Foreign Stock | Quoted Prices In Active Markets (Level 1) | Supplemental Executive Retirement Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		183
American Depository Receipts | Supplemental Executive Retirement Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		1,429
American Depository Receipts | Quoted Prices In Active Markets (Level 1) | Supplemental Executive Retirement Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		1,429
Preferred American Depository Receipts | Supplemental Executive Retirement Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		12
Preferred American Depository Receipts | Quoted Prices In Active Markets (Level 1) | Supplemental Executive Retirement Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		12
Real Estate Investment Trusts | Supplemental Executive Retirement Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		72
Real Estate Investment Trusts | Quoted Prices In Active Markets (Level 1) | Supplemental Executive Retirement Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		72
Open Ended Mutual Funds | Supplemental Executive Retirement Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		1,676
Open Ended Mutual Funds | Supplemental Executive Retirement Plan | Measured At Net Asset Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets		$ 1,676