Pensions - Pension Plan Assets at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value Of Pension Plan Assets [Line Items]
Pension plan assets at fair value	$ 299,419	$ 312,711
Equity securities [Member]
Fair Value Of Pension Plan Assets [Line Items]
Pension plan assets at fair value	36,739	36,017
Debt securities [Member]
Fair Value Of Pension Plan Assets [Line Items]
Pension plan assets at fair value	34,680	30,770
Cash and cash equivalents [Member]
Fair Value Of Pension Plan Assets [Line Items]
Pension plan assets at fair value	2,555	2,927
Net Asset Value [Member]
Fair Value Of Pension Plan Assets [Line Items]
Pension plan assets at fair value	225,445	242,997
Net Asset Value [Member] | Equity securities [Member]
Fair Value Of Pension Plan Assets [Line Items]
Pension plan assets at fair value	101,053	103,105
Net Asset Value [Member] | Debt securities [Member]
Fair Value Of Pension Plan Assets [Line Items]
Pension plan assets at fair value	98,967	109,372
Net Asset Value [Member] | Real Estate [Member]
Fair Value Of Pension Plan Assets [Line Items]
Pension plan assets at fair value	25,425	30,520
Level 1 [Member]
Fair Value Of Pension Plan Assets [Line Items]
Pension plan assets at fair value	19,168	22,022
Level 1 [Member] | Equity securities [Member]
Fair Value Of Pension Plan Assets [Line Items]
Pension plan assets at fair value	16,613	15,991
Level 1 [Member] | Debt securities [Member]
Fair Value Of Pension Plan Assets [Line Items]
Pension plan assets at fair value	0	3,104
Level 1 [Member] | Cash and cash equivalents [Member]
Fair Value Of Pension Plan Assets [Line Items]
Pension plan assets at fair value	2,555	2,927
Level 2 [Member]
Fair Value Of Pension Plan Assets [Line Items]
Pension plan assets at fair value	54,806	47,692
Level 2 [Member] | Equity securities [Member]
Fair Value Of Pension Plan Assets [Line Items]
Pension plan assets at fair value	20,126	20,026
Level 2 [Member] | Debt securities [Member]
Fair Value Of Pension Plan Assets [Line Items]
Pension plan assets at fair value	34,680	27,666
Level 2 [Member] | Cash and cash equivalents [Member]
Fair Value Of Pension Plan Assets [Line Items]
Pension plan assets at fair value	$ 0	$ 0