Comprehensive Income (Components Of Comprehensive Income, Net Of Related Tax) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Net income	$ 30,743	$ 23,773	$ 81,455	$ 63,310
Arising during the period, net of tax expense of $1,061, $171, $2,989 and $1,647	1,970	318	5,779	3,059
Less: reclassification adjustment for gains (losses) included in net income, net of tax (benefit) expense of $(65), $8, $124 and $50	120	(16)	(459)	(92)
Pension and postretirement amortization, net of tax expense of $161, $90, $461 and $279	299	166	856	517
Other comprehensive income	2,389	468	6,176	3,484
Comprehensive income	$ 33,132	$ 24,241	$ 87,631	$ 66,794