Accumulated Other Comprehensive Income, Net of Tax (Schedule of Accumulated Other Comprehensive Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense	$ (33,991)	$ (14,802)	$ (64,202)	$ (25,946)
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense	0		0	(2)
Net of tax	0	0	0	6
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member] | Reclassification out of accumualted comprehensive income [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Debt Securities, Available-for-sale, Gain (Loss)	0	0	0	8
Income tax expense		0
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Net of tax	(823)	(1,415)	(1,621)	(2,868)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of accumualted comprehensive income [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense	291	501	574	1,015
Net of tax	(823)	(1,415)	(1,621)	(2,868)
Other Nonoperating Expense	(1,037)	(1,088)	(2,042)	(2,261)
Interest Income, Other	(77)	(828)	(153)	(1,622)
Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	(1,007)	(990)	(2,015)	(1,980)
Defined benefit pension and postretirement benefit plans [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Net of tax	(741)	(730)	(1,484)	(1,459)
Income tax expense	$ 266	$ 260	$ 531	$ 521