Capital and Regulatory Matters (Narrative) (Detail)						12 Months Ended
	Feb. 15, 2016 USD ($)	Jan. 01, 2016	Aug. 13, 2013 shares	Feb. 15, 2013 USD ($) $ / shares shares	Feb. 12, 2013 USD ($) shares	Dec. 31, 2015 USD ($) quarter $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) shares	Jan. 01, 2019	Apr. 30, 2015 USD ($)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Non-cumulative perpetual preferred stock						$ 144,500,000
Non-cumulative perpetual preferred stock, dividend rate percentage						5.375%
Trust preferred securities						$ 133,000,000
Corporation's aggregate subordinated notes						$ 137,115,000	$ 137,115,000
Preferred stock, shares issued | shares						6,000,000	6,000,000
Preferred stock, par value | $ / shares						$ 0.01	$ 0.01
Proceeds from issuance of preferred stock				$ 144,500,000		$ 0	$ 0	$ 144,486,000
Accelerated share repurchase authorized amount										$ 100,000,000
Stock repurchase program, period in force						2 years
Treasury stock, shares, acquired | shares						1,504,146	18,871	2,245,572
Treasury stock, value, acquired, cost method						$ (101,237,000)	$ (1,457,000)	$ (144,630,000)
Amount paid under accelerated share repurchase agreement					$ 144,000,000
Shares repurchased under accelerated share repurchase program | shares			331,671		1,905,077
Accelerated Share Repurchase Program Repurchase Share Percent					80.00%
Aggregate dividends available for payment without prior regulatory approval						$ 419,700,000
Maximum number of quarterly periods by which the corporation has the right to defer interest payments on junior subordinated deferrable interest debentures | quarter						20
Two Thousand And Nineteen [Member] | Scenario, Forecast [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Risk Based Capital To Risk Weighted Assets Minimum Capital Required Basel III Phase In Schedule									4.50%
Capital Conservation Buffer									2.50%
Minimum ratio of Tier 1 capital to risk-weighted assets									6.00%
Minimum ratio of Total capital to risk weighted assets									8.00%
Two Thousand And Nineteen [Member] | Scenario, Forecast [Member] | Minimum [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Effective common equity tier one capital to risk weighted assets, ratio upon full implementation									7.00%
Effective tier one capital ratio, upon full implementation									8.50%
Tier one risk based capital to risk weighted assets, ratio upon full implementation									10.50%
Minimum leverage ratio									4.00%
Two Thousand And Sixteen [Member] | Scenario, Forecast [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier one capital conservation buffer to risk weighted assets required under regulatory		0.625%
Tier one risk based capital conservation buffer initial requirements phasing duration		4 years
Series A Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Non-cumulative perpetual preferred stock, dividend rate percentage				5.375%
Preferred stock, shares issued | shares				6,000,000
Series A Preferred Stock, Liquidation preference value				$ 150,000,000		$ 25	25
Preferred stock, par value | $ / shares				$ 0.01
Liquidation preference per share | $ / shares				$ 25
Treasury Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Treasury stock, shares, acquired | shares						1,485,493
Treasury stock, value, acquired, cost method						$ (100,000,000)
Trust Preferred Securities Tier One Allowable Portion [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust preferred securities						33,300,000
Trust Preferred Securities Tier Two Capital Allowable Portion [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust preferred securities						99,800,000
Floating Rate Subordinated Notes [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Corporation's aggregate subordinated notes						$ 100,000,000
Per year percentage of decreases in permissible portion of Subordinate Note included in Total Capital						20.00%
Final years of the term of the notes						5 years
Permissible portion of subordinated note included in total capital						$ 20,000,000	$ 40,000,000
Floating Rate Subordinated Notes [Member] | Two Thousand And Sixteen [Member] | Scenario, Forecast [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Permissible portion of subordinated note included in total capital	$ 0