Investment Securities (Narrative) (Detail) (USD $)	3 Months Ended			6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012	Jun. 30, 2013		Jun. 30, 2012	Dec. 31, 2012
Schedule of Investments [Line Items]
Callable securities				$ 779,300,000
Pledged securities as required or permitted by law	2,600,000,000			2,600,000,000			2,500,000,000
Percent of government obligations to consolidated shareholders' equity maximum	10.00%		10.00%	10.00%		10.00%
Gross Unrealized Losses	(58,758,000)			(58,758,000)			(31,489,000)
Proceeds from sales of available for sale securities	24,750,000		45,855,000	36,521,000		45,855,000
Securities available for sale, at fair value	3,257,360,000			3,257,360,000			3,136,160,000
Held-to-maturity securities unrealized loss	(43,743,000)			(43,743,000)			(592,000)
Percentage of bank qualified bonds with credit rating range of AAA to A				95.60%
Percentage Of Bank Qualified Bonds With Credit Rating Range Of A To AAA				97.30%
Percentage of municipal bond Portfolio comprised of General Obligation bonds				84.80%
Percentage of municipal bond portfolio comprised of Revenue bonds				14.80%
Percentage of municipal bond portfolio comprised of other bonds				0.40%
Private equity fund investments, fair value	12,600,000			12,600,000			12,100,000
Realized Loss on private equity funds, net of OTTI charges	20,000			284,000		257,000
Realized Gain on private equity funds, net of OTTI charges			503,000
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Categories of Investments [Domain]
Schedule of Investments [Line Items]
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held	10,460,000			10,460,000			(10,500,000)
Collateralized loan obligations (CLOs) [Member]
Schedule of Investments [Line Items]
Gross Unrealized Losses	(474,000)			(474,000)			(225,000)
Securities available for sale, at fair value	278,008,000			278,008,000			88,540,000
Pooled trust preferred securities [Member]
Schedule of Investments [Line Items]
Gross Unrealized Losses	(13,810,000)	[1]		(13,810,000)	[1]		(19,811,000)	[2]
Increase in pooled issuers trust preferred securities				4,000,000
Securities available for sale, at fair value	30,215,000	[1]		30,215,000	[1]		26,207,000	[2]
Decrease in available-for-sale securities, gross unrealized loss				(6,000,000)
Single issuer trust preferred securities [Member]
Schedule of Investments [Line Items]
Gross Unrealized Losses	(6,392,000)			(6,392,000)			(6,766,000)
Securities available for sale, at fair value	44,875,000			44,875,000			44,415,000
Decrease in available-for-sale securities, gross unrealized loss				(500,000)
Number of investments issued				5
Number of large capitalization money center financial institutions				3
Corporate debt securities [Member]
Schedule of Investments [Line Items]
Number of unrealized loss positions	1			1
Gross Unrealized Losses	(146,000)			(146,000)			0	[3]
Securities available for sale, at fair value	112,671,000			112,671,000			118,199,000
Equity securities [Member]
Schedule of Investments [Line Items]
Gross Unrealized Losses	0	[3]		0	[3]
Agency CMOs [Member]
Schedule of Investments [Line Items]
Gross Unrealized Losses	(727,000)			(727,000)			(92,000)
Securities available for sale, at fair value	1,003,897,000			1,003,897,000			1,310,006,000
Held-to-maturity securities unrealized loss	(801,000)			(801,000)			(8,000)
Number of Securities	1			1
Agency mortgage-backed securities [Member]
Schedule of Investments [Line Items]
Gross Unrealized Losses	(36,312,000)			(36,312,000)			(1,098,000)
Proceeds from sales of available for sale securities	0		0	11,771,000		0
Securities available for sale, at fair value	1,338,192,000			1,338,192,000			1,142,280,000
Held-to-maturity securities unrealized loss	(37,413,000)			(37,413,000)			(474,000)
Municipal bonds and notes [Member]
Schedule of Investments [Line Items]
Held-to-maturity securities unrealized loss	(362,000)			(362,000)			(110,000)
CMBS [Member]
Schedule of Investments [Line Items]
Number of unrealized loss positions	9			9
Gross Unrealized Losses	(897,000)			(897,000)			(3,493,000)
Proceeds from sales of available for sale securities	24,750,000		16,284,000	24,750,000		16,284,000
Securities available for sale, at fair value	440,136,000			440,136,000			398,031,000
Held-to-maturity securities unrealized loss	$ (5,167,000)			$ (5,167,000)			$ 0

[1] Amortized cost is net of $10.5 million of credit related other-than-temporary impairment at June 30, 2013.

[2] Amortized cost is net of $10.5 million of credit related other-than-temporary impairment at December 31, 2012.

[3] Amortized cost is net of $21.3 million of other-than-temporary impairment at December 31, 2012.