Net Income Per Common Share and Other Comprehensive Income Components of Other Comprehensive Income (Details) (USD $)	9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract]
Unrealized gain on securities, net of tax	$ 15,143,000		$ 30,390,000
Unrealized gain on securities, tax	8,200,000		16,400,000
Non-credit related unrealized gain (loss) on other-than-temporarily impaired debt securities, net of tax	187,000		(1,886,000)
Non-credit related unrealized gain (loss) on other-than-temporarily impaired debt securities, tax	100,000		1,000,000
Unrealized gain on derivative financial instruments, net of tax	102,000	[1]	102,000	[1]
Unrealized gain on derivative financial instruments, tax	55,000		55,000
(Accretion) amortization of net unrecognized pension and postretirement items, net of tax	(37,000)		55,000
Amortization of unrecognized pension and postretirement costs, tax	19,000		30,000
Reclassification adjustment for securities (gains) losses included in net income, net of tax	(979,000)		(329,000)
Reclassification adjustment for securities (gains) losses included in net income, tax	527,000		177,000
Other comprehensive income	14,416,000		28,332,000
Net losses in accumulated other comprehensive income reclassified into earnings during the next 12 months	$ 135,000

[1] Amounts represent the amortization of the effective portions of losses on forward-starting interest rate swaps, designated as cash flow hedges and entered into in prior years in connection with the issuance of fixed-rate debt. The total amount recorded as a reduction to accumulated other comprehensive income upon settlement of these derivatives is being amortized to interest expense over the life of the related securities using the effective interest method. The amount of net losses in accumulated other comprehensive income that will be reclassified into earnings during the next twelve months is expected to be approximately $135,000.