Shareholders' Equity (Details) (USD $)	0 Months Ended		1 Months Ended			3 Months Ended	12 Months Ended
	Nov. 07, 2013	Nov. 13, 2012	Dec. 31, 2013	Nov. 30, 2013	Oct. 31, 2013	Dec. 31, 2013	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011		Jan. 24, 2008
Shareholders' Equity
Percentage of dividend on preferred stock	6.75%	5.50%
Preferred stock, liquidation preference per share (in dollars per share)	$ 1,000	$ 1,000
Components of AOCI
Net unrealized (loss) gain on securities available-for-sale			$ (15,641,000)			$ (15,641,000)	$ (15,641,000)		$ 86,526,000
Net unrealized gain on cash flow hedges									56,000
Total accumulated other comprehensive (loss) income			(15,641,000)			(15,641,000)	(15,641,000)		86,582,000
Securities available-for-sale:
Net unrealized losses arising during the period							(168,824,000)		24,020,000		72,499,000
Reclassification adjustment for net gains included in net income							(6,811,000)		(183,000)		(4,955,000)
Non-credit related impairment loss									(988,000)		(4,198,000)
Total securities available for sale							(175,635,000)		22,849,000		63,346,000
Net change on cash flow hedges							(56,000)		(166,000)		(962,000)
Pension liability adjustment									1,085,000		(368,000)
Total other comprehensive (losses) income							(175,691,000)		23,768,000		62,016,000
Components and related tax effects of other comprehensive income
Net unrealized (losses) gains arising during the period							(70,619,000)		10,047,000		30,326,000
Reclassification adjustment for net gains included in net income, taxes							(2,849,000)		(76,000)		(2,073,000)
Non-credit related impairment loss, taxes									(413,000)		(1,756,000)
Total securities available for sale							(73,468,000)		9,558,000		26,497,000
Total other comprehensive (loss) income							(73,468,000)		9,558,000		26,497,000
Components and related tax effects of other comprehensive income
Net unrealized (losses) gains arising during the period							(98,205,000)		13,973,000		42,173,000
Reclassification adjustment for net gains/losses included in net income							(3,962,000)		(107,000)		(2,882,000)
Non-credit related impairment loss									(575,000)		(2,442,000)
Total securities available for sale							(102,167,000)		13,291,000		36,849,000
Net change on cash flow hedges							(56,000)	[1]	(166,000)	[1]	(962,000)	[1]
Pension liability adjustment									1,085,000		(368,000)
Total other comprehensive (loss) income							(102,223,000)		14,210,000		35,519,000
Number of shares authorized to be repurchased													1,000,000
Number of shares that may yet be purchased			1,140,400			1,140,400	1,140,400
Number of shares received in payment for exercise price of stock options exercised							0
Common shares repurchased
Total number of Shares (or Units) Purchased			421	28	233	682
Average Price Paid per Share (or Unit) (in dollars per share)			$ 77.35	$ 74.39	$ 70.27	$ 74.81
Depositary shares
Shareholders' Equity
Depositary shares of preferred stock issued	4,000,000	7,000,000
Interest of each depositary share in a share of preferred stock public offered	0.025	0.025
Depositary shares (in dollars per share)	$ 25.00	$ 25.00
Net proceeds from issuance of depositary shares	$ 97,700,000	$ 169,900,000
Preferred stock, redemption period	10 years	5 years
Depositary shares | LIBOR
Shareholders' Equity
Preferred stock, variable rate basis	three-month LIBOR
Preferred stock, basis spread (as a percent)	4.052%

[1] See Note 16 for additional information on other comprehensive income related to cash flow hedges.