Investment Securities - Amortized Cost, Gross Unrealized Gains and Losses and Fair Value of Securities Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 813,474		$ 598,837
Gross Unrealized Gains	13,821		17,428
Gross Unrealized Losses	(19,479)		(49,745)
Fair Value	807,816		566,520
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	99,843
Gross Unrealized Gains
Gross Unrealized Losses	(2,218)
Fair Value	97,625
U.S. government agency securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	44,215		89,787
Gross Unrealized Gains	1,547		1,204
Gross Unrealized Losses			(243)
Fair Value	45,762		90,748
Obligations of states and political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	16,210		18,893
Gross Unrealized Gains	417		1,322
Gross Unrealized Losses			(1)
Fair Value	16,627		20,214
Residential mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	506,695		304,631
Gross Unrealized Gains	6,818		10,950
Gross Unrealized Losses	(3,359)		(5,444)
Fair Value	510,154		310,137
Trust preferred securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	68,931	[1]	106,931	[1]
Gross Unrealized Gains	240	[1]	78	[1]
Gross Unrealized Losses	(11,739)	[1]	(36,585)	[1]
Fair Value	57,432	[1]	70,424	[1]
Corporate and other debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	28,274		30,663
Gross Unrealized Gains	2,728		2,554
Gross Unrealized Losses	(294)		(173)
Fair Value	30,708		33,044
Equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	49,306		47,932
Gross Unrealized Gains	2,071		1,320
Gross Unrealized Losses	(1,869)		(7,299)
Fair Value	$ 49,508		$ 41,953

[1] Includes three pooled trust preferred securities, principally collateralized by securities issued by banks and insurance companies.