Comprehensive Income (Components Of Comprehensive Income, Net Of Related Tax) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease [Abstract]
Net income	$ 28,538	$ 21,582
Unrealized gains on securities, Arising during the period, net of tax (benefit) expense of $(99) and $649	(184)	1,205
Less: reclassification adjustment for gains included in net income, net of tax expense of $239 and $38	(445)	(70)
Unrealized losses on derivative instruments, net of tax benefit of $373	(694)
Unrealized losses associated with pension and postretirement benefits, net of tax benefit of $188 and $150	349	278
Other comprehensive income	(974)	1,413
Comprehensive income	$ 27,564	$ 22,995