Postretirement Benefit Plans - Defined Contribution Expenses for Company's Qualified Defined Contribution Plans and Statutory Profit Sharing Contributions (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Contribution Plan Disclosure [Line Items]
Total defined contribution expense	$ 12,030	$ 11,799	$ 12,000
Retirement Contributions [Member]
Defined Contribution Plan Disclosure [Line Items]
Total defined contribution expense	7,328	7,617	4,998
Profit Sharing Contributions [Member]
Defined Contribution Plan Disclosure [Line Items]
Total defined contribution expense	$ 4,702	$ 4,182	$ 7,002