Accumulated Other Comprehensive Income (Loss) (Reclassifications Out of AOCI) (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amortization of net actuarial loss		$ (915)
Amortization of prior service credit		1,018
Reclassifications out of AOCI		62	$ (729)
Unrealized gains (losses) on debt securities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net realized losses on sales of debt securities		(41)	(569)
Reclassifications out of AOCI		(41)	(569)
Tax effect		10	132
Pension Benefit Adjustment
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amortization of net actuarial loss	[1]	(915)	(1,205)
Amortization of prior service credit	[1]	1,018	1,045
Reclassifications out of AOCI	[1]	103	(160)
Tax effect	[1]	$ (27)	$ 40

[1] These components of AOCI are components of net periodic cost. See Note 10 Employee Benefit Plans for additional details.