Benefit Plans (Narrative) (Details) (USD $)	12 Months Ended				12 Months Ended									12 Months Ended						12 Months Ended													3 Months Ended	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2011 Equity Securities [Member]	Dec. 31, 2011 Fixed Income Securities [Member]	Dec. 31, 2011 Preferred Stock [Member]	Dec. 31, 2010 Preferred Stock [Member]	Dec. 31, 2011 Non Funded Directors' Retirement Plan [Member]	Dec. 31, 2010 Non Funded Directors' Retirement Plan [Member]	Dec. 31, 2009 Non Funded Directors' Retirement Plan [Member]	Dec. 31, 2011 Non-Qualified Plans For Former Directors [Member]	Dec. 31, 2010 Non-Qualified Plans For Former Directors [Member]	Dec. 31, 2011 Funded Plans For Former Directors [Member]	Dec. 31, 2010 Funded Plans For Former Directors [Member]	Dec. 31, 2011 Employee Stock Option [Member]	Dec. 31, 2010 Employee Stock Option [Member]	Dec. 31, 2009 Employee Stock Option [Member]	Dec. 31, 2011 Stock Awards [Member]	Dec. 31, 2011 Stock Options [Member] years	Dec. 31, 2010 Stock Options [Member]	Dec. 31, 2009 Stock Options [Member]	Dec. 31, 2011 Non Vested Stock Options [Member] years	Dec. 31, 2010 Non Vested Stock Options [Member]	Dec. 31, 2009 Non Vested Stock Options [Member]	Dec. 31, 2011 Restricted Stock [Member] years	Dec. 31, 2010 Restricted Stock [Member]	Dec. 31, 2009 Restricted Stock [Member]	Dec. 31, 2011 Consumer Price Index [Member] Equity Securities [Member]	Dec. 31, 2011 Consumer Price Index [Member] Fixed Income Securities [Member]	Dec. 31, 2011 S&P 500 Index [Member] Equity Securities [Member]	Dec. 31, 2011 Merrill Lynch Intermediate Government/Corporate Index [Member] Fixed Income Securities [Member]	Mar. 31, 2012 Defined Benefit Plan Contribution [Member]	Dec. 31, 2011 Decrease In Expected Rate [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Accumulated other comprehensive loss recognize net actuarial loss	$ 2,300,000
Accumulated other comprehensive loss recognize prior service cost	707,000
Asset allocation for qualified plan, equity securities, minimum	25.00%
Asset allocation for qualified plan, equity securities, maximum	65.00%
Asset allocation for qualified plan, fixed income securities, minimum	35.00%
Asset allocation for qualified plan, fixed income securities, maximum	75.00%
Cumulative annual real return					7.00%	3.00%
Cumulative annual real return, period																													5	5	3	3
Preferred securities							62,752	62,752
Shares, fair values							1,600,000	1,600,000
Dividends received on preferred shares							122,000	122,000
Expected contribution based upon actuarial estimates	16,678,000	2,243,000
Projected benefit obligation	120,564,000	96,360,000							1,900,000	1,800,000		6,600,000	7,500,000	4,000,000	4,700,000
Discount rate used to compute the obligation	5.75%	6.00%	5.75%						4.87%	5.75%
Obligation included in other liabilities									468,000	419,000				1,500,000	1,600,000
Obligation included in other liabilities, net of tax									252,000	226,000				1,100,000	1,200,000
Expense recognized for the Directors' retirement plan									232,000	228,000	250,000
Accumulated other comprehensive loss	(62,441,000)	(5,719,000)	(19,816,000)	(60,931,000)										1,500,000
Salary expense																4,000,000	6,600,000	2,400,000
Expense for contributions to the plan	2,000,000	1,900,000	1,400,000
Award shares to its employees																			7,100,000
Incentive stock options maximum term, years		ten years
Stock-based compensation expense	3,156,000	4,830,000	5,049,000																	3,300,000	4,800,000	5,000,000
Stock awards granted																					1,300,000	599,000
Stock-based compensation																				2,000,000			169,000			1,600,000
Average remaining vesting, years																				2			1			1.6
Cash received from stock options exercised																								290,000	61,000
Compensation costs related to restricted stock awards																										2,900,000	3,900,000	3,900,000
Expected return on plan assets	8.00%	8.00%	8.00%																															7.50%
Employer contributions	$ 13,105,000	$ 5,096,000																															$ 25,000,000