Investment Securities (Narrative) (Detail) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012	Dec. 31, 2012
Schedule of Investments [Line Items]
Securities available for sale, at fair value	$ 3,193,772,000			$ 3,193,772,000			$ 3,136,160,000
Pledged securities as required or permitted by law	2,900,000,000			2,900,000,000			2,500,000,000
Investments in obligations of individual states, counties or municipalities	6,387,392,000			6,387,392,000			6,176,711,000
Unrealized loss	(52,549,000)			(52,549,000)			(31,489,000)
Number of positions	133			133			54
Held-to-maturity securities unrealized loss	(41,095,000)			(41,095,000)			(592,000)
Number of unrealized loss positions	120			120			24
US Treasury Bill Securities [Member]
Schedule of Investments [Line Items]
Securities available for sale, at fair value	849,700,000			849,700,000
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Investments in obligations of individual states, counties or municipalities	0			0			0
Agency collateralized mortgage obligations (CMOs) [Member]
Schedule of Investments [Line Items]
Securities available for sale, at fair value	885,476,000			885,476,000			1,310,006,000
Unrealized loss	(1,349,000)			(1,349,000)			(92,000)
Number of positions	6			6			4
Held-to-maturity securities unrealized loss	(492,000)			(492,000)			(8,000)
Number of unrealized loss positions	2			2			1
Collateralized loan obligations (CLOs) [Member]
Schedule of Investments [Line Items]
Securities available for sale, at fair value	332,534,000			332,534,000			88,540,000
Unrealized loss	(1,126,000)			(1,126,000)			(225,000)
Number of positions	14			14			2
Pooled trust preferred securities [Member]
Schedule of Investments [Line Items]
Securities available for sale, at fair value	29,964,000	[1]		29,964,000	[1]		26,207,000	[2]
Unrealized loss	(6,617,000)	[1]		(6,617,000)	[1]		(19,811,000)	[2]
Number of positions	6			6			8
Increase in pooled issuers trust preferred securities				3,800,000
Increase (decrease) in available-for-sale securities, gross unrealized loss				(13,200,000)
Average period for discount cash flows				6 months
Single issuer trust preferred securities [Member]
Schedule of Investments [Line Items]
Securities available for sale, at fair value	43,302,000			43,302,000			44,415,000
Unrealized loss	(8,009,000)			(8,009,000)			(6,766,000)
Number of positions	9			9			9
Increase in pooled issuers trust preferred securities				(1,100,000)
Increase (decrease) in available-for-sale securities, gross unrealized loss				(1,200,000)
Number of investments issued				5
Number of large capitalization money center financial institutions				3
Corporate debt securities [Member]
Schedule of Investments [Line Items]
Securities available for sale, at fair value	113,618,000			113,618,000			118,199,000
Unrealized loss	0			0			0
Equity securities - financial institutions [Member]
Schedule of Investments [Line Items]
Securities available for sale, at fair value	9,389,000	[3]		9,389,000	[3]		8,282,000	[4]
Unrealized loss	0	[3]		0	[3]		(4,000)	[4]
Number of positions							1
Agency MBS [Member]
Schedule of Investments [Line Items]
Securities available for sale, at fair value	1,293,254,000			1,293,254,000			1,142,280,000
Unrealized loss	(34,416,000)			(34,416,000)			(1,098,000)
Number of positions	92			92			28
Held-to-maturity securities unrealized loss	(35,832,000)			(35,832,000)			(474,000)
Number of unrealized loss positions	72			72			12
Municipal bonds and notes [Member]
Schedule of Investments [Line Items]
Held-to-maturity securities unrealized loss	(743,000)			(743,000)			(110,000)
Percentage of bank qualified bonds with credit rating range of AAA to A				93.90%
Percentage Of Bank Qualified Bonds With Credit Rating Range Of A To AAA				95.80%
Percentage of municipal bond Portfolio comprised of General Obligation bonds				85.00%
Percentage of municipal bond portfolio comprised of Revenue bonds				14.50%
Percentage of municipal bond portfolio comprised of other bonds				0.50%
Number of unrealized loss positions	38			38			11
CMBS [Member]
Schedule of Investments [Line Items]
Securities available for sale, at fair value	465,951,000			465,951,000			398,031,000
Unrealized loss	(1,032,000)			(1,032,000)			(3,493,000)
Number of positions	6			6			2
Held-to-maturity securities unrealized loss	(4,028,000)			(4,028,000)			0
Number of unrealized loss positions	8			8
Private Label MBS [Member]
Schedule of Investments [Line Items]
Held-to-maturity securities unrealized loss	0			0			0
Alternative Investments [Member]
Schedule of Investments [Line Items]
Alternative investments	19,000,000			19,000,000			19,500,000
Principal Investment Loss	$ 70,000		$ 518,000	$ 354,000		$ 775,000

[1] Amortized cost is net of $9.4 million of credit related other-than-temporary impairment at September 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 September 30, 2013.

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