Comprehensive Income (Components of Comprehensive Income, Net of Related Tax) (Details) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Comprehensive Income
Net income	$ 22,362	$ 17,922	$ 39,537	$ 33,902
Arising during the period, net of tax expense of $1,515, $1,613, $1,467 and $2,091	2,814	2,996	2,725	3,883
Less: reclassification adjustment for gains included in net income, net of tax expense (benefit) of $13, $(194), $32 and $52	(25)	360	(60)	(97)
Pension and postretirement amortization, net of tax expense of $94, $671, $189 and $802	174	1,246	351	1,489
Other comprehensive income	2,963	4,602	3,016	5,275
Comprehensive income	25,325	22,524	42,553	39,177
Other comprehensive income (loss), tax expense (benefit) on unrealized holding gain (loss) on securities arising during period	1,515	1,613	1,467	2,091
Other comprehensive income (loss), tax expense (benefit) on reclassification adjustment included in net income	13	(194)	32	52
Other comprehensive income (loss), tax expense (benefit) on pension and postretirement amortization	$ 94	$ 671	$ 189	$ 802