Employee Benefit Plans - Return on Current and Target Asset Allocation (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	$ 23,749	$ 25,646
Total fair value of plan assets, not including pooled funds	6,126	6,164
Pooled funds	17,623	19,482
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	153	135
Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	3,647	3,494
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	1,475	1,625
Other Investments
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	851	910
Level 1
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan assets, not including pooled funds	6,126	6,164
Level 1 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	153	135
Level 1 | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	3,647	3,494
Level 1 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	1,475	1,625
Level 1 | Other Investments
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	851	910
Level 2
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan assets, not including pooled funds	0	0
Level 2 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Level 2 | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Level 2 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Level 2 | Other Investments
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Level 3
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan assets, not including pooled funds	0	0
Level 3 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Level 3 | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Level 3 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0	0
Level 3 | Other Investments
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	$ 0	$ 0