Pension and Other Post-Retirement Benefits (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Pension Benefits
Components of net periodic (credit) expense:
Interest cost	[1]	$ 1,415	$ 1,271	$ 2,830	$ 2,543
Expected return on plan assets	[1]	(3,483)	(4,035)	(6,966)	(8,071)
Amortization of prior-service costs	[1]	0	0	0	0
Amortization of net actuarial loss	[1]	2,509	1,795	5,018	3,591
Net periodic expense (credit)	[1]	441	(969)	882	(1,937)
Post- Retirement Benefits
Components of net periodic (credit) expense:
Interest cost	[1]	128	128	256	256
Expected return on plan assets	[1]	0	0	0	0
Amortization of prior-service costs	[1]	(62)	(62)	(124)	(124)
Amortization of net actuarial loss	[1]	31	76	62	153
Net periodic expense (credit)	[1]	$ 97	$ 142	$ 194	$ 285

[1] Amounts are included in G&A expense on the Consolidated Statements of Income and Comprehensive Income.