Accumulated Other Comprehensive Income (Loss) - Summary of Amounts Reclassifications Out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Income applicable to common stock	[1]	$ (568)	$ (750)	$ (1,134)	$ (1,500)
Interest, net		(3,417)	(2,869)	(7,031)	(6,923)
Tax benefit		(11,326)	(7,205)	(24,137)	(16,455)
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amortization of defined benefit pension actuarial losses	[1],[2]	(902)	(1,195)	(1,804)	(2,389)
Defined Benefit Pension Plan Adjustments [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Income applicable to common stock		(565)	(750)	(1,129)	(1,499)
Defined Benefit Pension Plan Adjustments [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Tax benefit	[1]	337	445	675	890
Income applicable to common stock	[1]	(565)	(750)	(1,129)	(1,499)
Cash Flow Hedge Adjustments [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Total before tax	[1]	(5)	(2)	(9)	(5)
Tax benefit	[1]	2	2	4	4
Income applicable to common stock	[1]	(3)		(5)	(1)
Cash Flow Hedge Adjustments [Member] | Interest rate contracts [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Interest, net	[1]	(7)	(5)	(13)	(10)
Cash Flow Hedge Adjustments [Member] | Commodity Contract [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Cost of sales	[1]	$ 2	$ 3	$ 4	$ 5

[1] Amounts in parentheses denote expense to statement of income.

[2] This component of accumulated other comprehensive income is included in the computation of net periodic benefit cost (see Note 8 for additional details).