Benefit Plans - Assets Measured at Fair Value on Recurring Basis (Detail) - Pension - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Total investments	$ 49,932	$ 43,449	$ 46,870	$ 43,153
Level 1
Defined Benefit Plan Disclosure [Line Items]
Total investments	24,636	21,897
Level 2
Defined Benefit Plan Disclosure [Line Items]
Total investments	25,296	21,552
Level 3
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Group annuity contracts
Defined Benefit Plan Disclosure [Line Items]
Total investments	81	100
Group annuity contracts | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Group annuity contracts | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total investments	81	100
Group annuity contracts | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Total investments	24,636	21,897
Mutual funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total investments	24,636	21,897
Mutual funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Mutual funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Fixed income
Defined Benefit Plan Disclosure [Line Items]
Total investments	16,609	15,252
Fixed income | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total investments	16,609	15,252
Fixed income | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Fixed income | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
International equity
Defined Benefit Plan Disclosure [Line Items]
Total investments	5,535	4,649
International equity | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total investments	5,535	4,649
International equity | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
International equity | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Large US equity
Defined Benefit Plan Disclosure [Line Items]
Total investments	1,496	1,224
Large US equity | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total investments	1,496	1,224
Large US equity | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Large US equity | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Small/Mid U.S. equity
Defined Benefit Plan Disclosure [Line Items]
Total investments	996	772
Small/Mid U.S. equity | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total investments	996	772
Small/Mid U.S. equity | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Small/Mid U.S. equity | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Pooled Separate Accounts
Defined Benefit Plan Disclosure [Line Items]
Total investments	25,215	21,452
Pooled Separate Accounts | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Pooled Separate Accounts | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total investments	25,215	21,452
Pooled Separate Accounts | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total investments	$ 0	$ 0