Benefit Plans - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Net actuarial loss expected to be recognized as a component of net periodic pension expense during 2013	$ 3,000,000
Prior service cost expected to be recognized as a component of net periodic pension expense during 2013	38,000	(11,161,000)
Projected benefit obligation	141,889,000	120,564,000
Discount rate used to compute the obligation	4.87%	5.75%	6.00%
Obligation included in other liabilities	19,707,000	38,050,000
Salary expense	7,400,000	4,000,000	6,600,000
Expense for contributions to savings and investment plan	2,700,000	2,000,000	1,900,000
Number of shares authorized under stock incentive plan	7,400,000
Stock-based compensation expense	4,816,000	3,156,000	4,830,000
Stock-based compensation	11,200,000
Average remaining vesting, years	5 years
Number of shares outstanding and exercisable	2,435,051	2,737,814	3,002,736
Number of shares exercised			26,070
Maximum [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Incentive stock options maximum term, years	10 years
Non-funded directors' retirement plan [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Projected benefit obligation	2,500,000	1,900,000
Discount rate used to compute the obligation	4.26%	4.87%
Obligation included in other liabilities	855,000	468,000
Obligation included in other comprehensive loss, net of tax	460,000	252,000
Expense recognized for the Directors' retirement plan	251,000	232,000	228,000
Non-qualified plans for former directors [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Projected benefit obligation	5,800,000	6,600,000
Funded plans for former directors [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Projected benefit obligation	3,300,000	4,000,000
Obligation included in other comprehensive loss, net of tax	1,400,000	1,500,000
Obligation included in other comprehensive loss, tax	1,000,000	1,100,000
Preferred Stock [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Preferred securities	58,631	62,752
Dividends received on preferred shares	114,000	122,000
Stock Options And Restricted Stock [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Stock-based compensation expense	4,700,000	3,300,000	4,800,000
Stock awards granted	2,500,000		1,300,000
Stock Options [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Stock-based compensation	31,000
Average remaining vesting, years	1 year
Risk-free interest rate, Minimum			0.29%
Risk-free interest rate, Maximum			2.92%
Dividend yield			5.50%
Volatility			35.00%
Expected term (in years)			4 years 4 months 24 days
Restricted Stock [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Stock-based compensation	11,000,000
Average remaining vesting, years	4 years 10 months 24 days
Compensation costs related to restricted stock awards	4,600,000	2,900,000	3,900,000
Stock Incentive Plan [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Number of outstanding and vested incentive stock options		356,000
Number of shares outstanding and exercisable	321,000
Aggregate weighted average exercise price	$ 17
Aggregate weighted average remaining term	2 years 7 months 6 days
Number of shares exercised	1,000
Equity securities [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Target asset allocation for qualified plan, minimum	25.00%
Target asset allocation for qualified plan, maximum	65.00%
Cumulative annual real return	7.00%
Equity securities [Member] | Consumer Price Index [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Cumulative annual real return, period	5 years
Equity securities [Member] | S&P 500 Index [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Cumulative annual real return, period	3 years
Debt securities [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Target asset allocation for qualified plan, minimum	35.00%
Target asset allocation for qualified plan, maximum	75.00%
Fixed income securities [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Cumulative annual real return	3.00%
Fixed income securities [Member] | Consumer Price Index [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Cumulative annual real return, period	5 years
Fixed income securities [Member] | Merrill Lynch Intermediate Government/Corporate Index [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Cumulative annual real return, period	3 years
Trust Preferred Securities Subject to Mandatory Redemption [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Shares, fair values	$ 1,500,000	$ 1,600,000