Defined Benefit Pension Plan and Postretirement Benefits - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2020
Most Employees 401(k) Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
401(k) plan, most employees, maximum employer matching contribution, percent of employee's gross pay	4.00%
Most Employees 401(k) Plan [Member] | Next Eligible Compensation
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
401(k) plan, most employees, employer matching contribution, percent of match	50.00%
401(k) plan, most employees, employer matching contribution, percent of employees' gross pay	2.00%
Most Employees 401(k) Plan [Member] | First Eligible Compensation
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
401(k) plan, most employees, employer matching contribution, percent of match	100.00%
401(k) plan, most employees, employer matching contribution, percent of employees' gross pay	3.00%
Highly Compensated Employees 401(k) Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
401(k) plan, most employees, employer matching contribution, percent of match	50.00%
401(k) plan, most employees, employer matching contribution, percent of employees' gross pay	4.00%
401(k) plan, most employees, maximum employer matching contribution, percent of employee's gross pay	2.00%