Pension and Postretirement Benefits - Additional Information (Detail)	3 Months Ended		12 Months Ended
	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2019 USD ($) plan	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Total expenses associated with plan			$ 9,493,000	$ 10,157,000	$ 13,466,000
Active, tax-qualified, defined-benefit pension plan | plan			0
Pension expense		$ 7,200,000
Pension settlement expense	$ 5,300,000
Estimated net loss to be amortized out of AOCI over the next fiscal year			$ 4,789,000
Percentage of total invested plan assets			5.00%
Minimum | Corporate Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Maturity date			1 year
Maximum | Corporate Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Maturity date			30 years
Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Percentage of total invested plan assets			100.00%
Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Percentage of total invested plan assets			75.00%
Foreign Bonds
Defined Benefit Plan Disclosure [Line Items]
Percentage of bond portfolio, foreign bonds			20.00%
Residential Mortgage-Backed Securities | Minimum
Defined Benefit Plan Disclosure [Line Items]
Maturity date			1 year
Residential Mortgage-Backed Securities | Maximum
Defined Benefit Plan Disclosure [Line Items]
Maturity date			30 years
Postretirement Life and Health Benefits
Defined Benefit Plan Disclosure [Line Items]
Employer contribution for pension plan			$ 40
Accrued postretirement benefit obligation			4,687,000	6,085,000
Qualified Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Employer contribution for pension plan				60,000,000	25,023,000
Non-qualified Plans
Defined Benefit Plan Disclosure [Line Items]
Benefits paid			$ 8,703,000	$ 8,901,000	$ 12,212,000