Investment Securities (Narrative) (Detail) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013	Sep. 30, 2014		Sep. 30, 2013	Dec. 31, 2013
Schedule of Investments [Line Items]
Securities available-for-sale, at fair value	$ 2,873,886,000			$ 2,873,886,000			$ 3,106,931,000
Pledged securities as required or permitted by law	2,900,000,000			2,900,000,000			2,700,000,000
Gross Unrealized Losses	(27,779,000)			(27,779,000)			(61,626,000)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	(27,259,000)			(27,259,000)			(61,218,000)
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(27,259,000)			(27,259,000)			(61,218,000)
Recognized other-than-temporary impairment	(85,000)		0	(246,000)		0
Callable at the option of the counterparty [Member]
Schedule of Investments [Line Items]
Securities available-for-sale, at fair value	818,000,000			818,000,000
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	638,223,000			638,223,000			806,912,000
Gross Unrealized Losses	(1,057,000)			(1,057,000)			(1,868,000)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	(1,409,000)			(1,409,000)			(1,009,000)
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(1,409,000)			(1,409,000)			(1,009,000)
Agency MBS [Member]
Schedule of Investments [Line Items]
Securities available-for-sale, at fair value	1,090,820,000			1,090,820,000			1,226,702,000
Gross Unrealized Losses	(23,539,000)			(23,539,000)			(47,698,000)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	(23,068,000)			(23,068,000)			(53,188,000)
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(23,068,000)			(23,068,000)			(53,188,000)
Agency commercial mortgage-backed securities (ACMBS) [Member]
Schedule of Investments [Line Items]
Securities available-for-sale, at fair value	80,383,000			80,383,000			70,977,000
Gross Unrealized Losses	(349,000)			(349,000)			(782,000)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	(622,000)			(622,000)			(818,000)
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(622,000)			(622,000)			(818,000)
Commercial mortgage-backed securities (CMBS) [Member]
Schedule of Investments [Line Items]
Securities available-for-sale, at fair value	532,842,000			532,842,000			464,274,000
Gross Unrealized Losses	(55,000)			(55,000)			(996,000)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	(2,122,000)			(2,122,000)			(4,975,000)
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(2,122,000)			(2,122,000)			(4,975,000)
Collateralized loan obligations (CLOs) [Member]
Schedule of Investments [Line Items]
Securities available-for-sale, at fair value	380,511,000	[1]		380,511,000	[1]		357,641,000	[2]
Gross Unrealized Losses	(142,000)	[1]		(142,000)	[1]		0	[2]
Pooled trust preferred securities [Member]
Schedule of Investments [Line Items]
Securities available-for-sale, at fair value	0			0			28,490,000	[3]
Gross Unrealized Losses	0	[3]		0	[3]		(3,410,000)	[3]
Single issuer trust preferred securities [Member]
Schedule of Investments [Line Items]
Securities available-for-sale, at fair value	39,382,000			39,382,000			34,935,000
Gross Unrealized Losses	(2,637,000)			(2,637,000)			(6,872,000)
Corporate debt securities [Member]
Schedule of Investments [Line Items]
Securities available-for-sale, at fair value	111,200,000			111,200,000			113,091,000
Gross Unrealized Losses	0			0			0
Equity securities - financial institutions [Member]
Schedule of Investments [Line Items]
Securities available-for-sale, at fair value	0			0			3,584,000	[4]
Gross Unrealized Losses	0			0			0	[4]
Municipal bonds and notes [Member]
Schedule of Investments [Line Items]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	(38,000)			(38,000)			(1,228,000)
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(38,000)			(38,000)			(1,228,000)
Percentage of bank qualified bonds with credit rating range of AAA to A				99.30%
Percentage of municipal bond Portfolio comprised of General Obligation bonds				86.00%
Percentage of municipal bond portfolio comprised of Revenue bonds				13.50%
Percentage of municipal bond portfolio comprised of other bonds				0.50%
Private Label MBS [Member]
Schedule of Investments [Line Items]
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	$ 0			$ 0			$ 0

[1] Amortized cost is net of $2.8 million of other-than-temporary impairments at September 30, 2014.

[2] Amortized cost is net of $2.6 million of other-than-temporary impairments at December 31, 2013.

[3] Amortized cost is net of $14.0 million of other-than-temporary impairments at December 31, 2013.

[4] Amortized cost is net of $20.4 million of other-than-temporary impairments at December 31, 2013.