Postretirement Benefit Plans - Defined Contribution Plans - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Contribution Plan Disclosure [Line Items]
Supplemental plan liability balances	$ 1,819	$ 1,519
Defined contribution plan expense	$ 12,030	11,799	$ 12,000
Percentage of union and non-union employees eligible for either statutory or Company's sponsored profit sharing contributions	77.00%
Statutory Plans [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan expense	$ 935	374	$ 398
Defined Contribution Plans [Member]
Defined Contribution Plan Disclosure [Line Items]
Balance of trust assets	$ 1,744	$ 1,444