Reclassifications Out of Accumulated Other Comprehensive Loss (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Prior service credit	$ (702)	$ (692)
Actuarial loss	3,835	3,253
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, before Tax, Total	3,133	2,561
Tax benefit	(1,240)	(1,013)
Amounts reclassified from accumulated other comprehensive loss, net of tax, Pension and Postretirement Benefit Plans	1,893	1,548
Additional interest expense	269	251
Tax benefit	(107)	(99)
Amounts reclassified from accumulated other comprehensive loss, net of tax, Unamortized Value of Terminated Forward Starting Interest Rate Swap	$ 162	$ 152