Weighted Average Asset Allocations for Retirement Plan (Detail)	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Weighted average asset allocation	100.00%	100.00%
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Weighted average asset allocation	58.00%	57.00%
Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Weighted average asset allocation	40.00%	41.00%
Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Weighted average asset allocation	2.00%	2.00%