Allowance For Loan Losses and Credit Quality Information (Allowance For Loan Losses And Loan Balances) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	$ 46,429		$ 56,248		$ 53,080		$ 60,339
Charge-offs	(6,870)		(9,965)		(40,048)		(30,084)
Recoveries	2,288		347		4,187		1,885
Provision	3,751		6,558		28,379		21,048
Ending balance	45,598		53,188		45,598		53,188
Loans individually evaluated for impairment	2,873				2,873
Specific reserves			7,347	[1]			7,347	[1]
Loans collectively evaluated for impairment	42,725				42,725
General reserves			45,841	[2]			45,841	[2]
Ending balance	45,598		53,188		45,598		53,188
Loans individually evaluated for impairment	50,164	[3]			50,164	[3]
Specific reserves			84,119	[1],[3]			84,119	[1],[3]
Loans collectively evaluated for impairment	2,651,595				2,651,595
General reserves			2,611,298	[2]			2,611,298	[2]
Ending balance	2,701,759		2,695,417		2,701,759		2,695,417
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	9,891		25,236		15,067		26,480
Charge-offs	(1,281)		(1,431)		(11,316)		(7,641)
Recoveries	455		71		1,305		409
Provision	(127)		1,645		3,882		6,273
Ending balance	8,938		25,521		8,938		25,521
Loans individually evaluated for impairment	1,244				1,244
Specific reserves			1,810	[1]			1,810	[1]
Loans collectively evaluated for impairment	7,694				7,694
General reserves			23,711	[2]			23,711	[2]
Ending balance	8,938		25,521		8,938		25,521
Loans individually evaluated for impairment	3,579	[3]			3,579	[3]
Specific reserves			21,270	[1],[3]			21,270	[1],[3]
Loans collectively evaluated for impairment	694,626				694,626
General reserves			1,376,272	[2]			1,376,272	[2]
Ending balance	698,205		1,397,542		698,205		1,397,542
Commercial Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	9,618		12,330		7,556		10,564
Charge-offs	(709)		(5,302)		(5,600)		(6,609)
Recoveries	18		94		382		381
Provision	(2,281)		302		4,308		3,088
Ending balance	6,646		7,424		6,646		7,424
Loans individually evaluated for impairment	90				90
Specific reserves			1,604	[1]			1,604	[1]
Loans collectively evaluated for impairment	6,556				6,556
General reserves			5,820	[2]			5,820	[2]
Ending balance	6,646		7,424		6,646		7,424
Loans individually evaluated for impairment	5,875	[3]			5,875	[3]
Specific reserves			20,306	[1],[3]			20,306	[1],[3]
Loans collectively evaluated for impairment	598,681				598,681
General reserves			583,564	[2]			583,564	[2]
Ending balance	604,556		603,870		604,556		603,870
Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	5,307		5,831		4,074		10,019
Charge-offs	(676)		(1,107)		(10,680)		(8,179)
Recoveries	1,314		51		1,642		557
Provision	(810)		926		10,099		3,304
Ending balance	5,135		5,701		5,135		5,701
Loans individually evaluated for impairment	94				94
Specific reserves			3,005	[1]			3,005	[1]
Loans collectively evaluated for impairment	5,041				5,041
General reserves			2,696	[2]			2,696	[2]
Ending balance	5,135		5,701		5,135		5,701
Loans individually evaluated for impairment	2,620	[3]			2,620	[3]
Specific reserves			21,701	[1],[3]			21,701	[1],[3]
Loans collectively evaluated for impairment	111,557				111,557
General reserves			89,803	[2]			89,803	[2]
Ending balance	114,177		111,504		114,177		111,504
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	6,265		3,707		6,544		4,028
Charge-offs	(705)		(877)		(3,344)		(2,183)
Recoveries	113		25		171		116
Provision	2,690		427		4,992		1,321
Ending balance	8,363		3,282		8,363		3,282
Loans individually evaluated for impairment	1,199				1,199
Specific reserves			808	[1]			808	[1]
Loans collectively evaluated for impairment	7,164				7,164
General reserves			2,474	[2]			2,474	[2]
Ending balance	8,363		3,282		8,363		3,282
Loans individually evaluated for impairment	18,072	[3]			18,072	[3]
Specific reserves			17,666	[1],[3]			17,666	[1],[3]
Loans collectively evaluated for impairment	232,270				232,270
General reserves			267,668	[2]			267,668	[2]
Ending balance	250,342		285,334		250,342		285,334
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	10,341		9,144		10,604		9,248
Charge-offs	(2,573)		(1,248)		(5,494)		(5,472)
Recoveries	204		106		497		422
Provision	4,300		3,258		6,665		7,062
Ending balance	12,272		11,260		12,272		11,260
Loans individually evaluated for impairment	24				24
Specific reserves			120	[1]			120	[1]
Loans collectively evaluated for impairment	12,248				12,248
General reserves			11,140	[2]			11,140	[2]
Ending balance	12,272		11,260		12,272		11,260
Loans individually evaluated for impairment	6,694	[3]			6,694	[3]
Specific reserves			3,176	[1],[3]			3,176	[1],[3]
Loans collectively evaluated for impairment	276,791				276,791
General reserves			293,991	[2]			293,991	[2]
Ending balance	283,485		297,167		283,485		297,167
Owner Occupied Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	4,091				9,235
Charge-offs	(926)				(3,614)
Recoveries	184				190
Provision	(4)				(2,466)
Ending balance	3,345				3,345
Loans individually evaluated for impairment	222				222
Loans collectively evaluated for impairment	3,123				3,123
Ending balance	3,345				3,345
Loans individually evaluated for impairment	13,324	[3]			13,324	[3]
Loans collectively evaluated for impairment	737,670				737,670
Ending balance	750,994				750,994
Complexity Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	916	[4]			0	[4]
Provision	(17)	[4]			899	[4]
Ending balance	899	[4]			899	[4]
Loans collectively evaluated for impairment	899	[4]			899	[4]
Ending balance	$ 899	[4]			$ 899	[4]

[1] Specific reserves represent loans individually evaluated for impairment.

[2] General reserves represent loans collectively evaluated for impairment.

[3] The difference between this amount and nonaccruing loans at September 30, 2012 and 2011, represents accruing troubled debt restructured loans.

[4] Represents the portion of the allowance for loan losses established to account for the inherent complexity and uncertainty of estimates.