Allowance For Loan Losses And Reserve For Unfunded Commitments (Allowance For Loan Losses and Recorded Investment in Loans) (Detail) - USD ($) $ in Thousands		3 Months Ended				6 Months Ended
		Jun. 30, 2015		Jun. 30, 2014		Jun. 30, 2015		Jun. 30, 2014		Dec. 31, 2014
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		$ 156,610		$ 146,768		$ 152,498		$ 143,109
Loans charged-off		(3,241)		(4,685)		(6,748)		(9,566)
Recoveries on loans previously charged-off		1,626		2,397		3,754		7,488
Net recoveries (charge-offs)		(1,615)		(2,288)		(2,994)		(2,078)
Provision (release) for loan losses		2,056		2,011		7,547		5,460
Balance at end of period		157,051		146,491		157,051		146,491
Ending balance, loans individually evaluated for impairment		7,468	[1]	18,487	[1]	7,468	[1]	18,487	[1]	$ 16,627
Ending balance, loans collectively evaluated for impairment		149,583		128,004		149,583		128,004
Recorded Investment in Loans: [Abstract]
Recorded Investment in Loans, Ending balance, loans individually evaluated for impairment		93,260	[1]	109,571	[1]	93,260	[1]	109,571	[1]	90,289
Recorded Investment in Loans, Ending balance, loans collectively evaluated for impairment		12,450,021		11,027,371		12,450,021		11,027,371
Total loans		12,543,281		11,136,942		12,543,281		11,136,942		11,892,219
Commercial [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		108,873		90,080		103,462		80,768
Loans charged-off		(2,921)		(2,142)		(5,123)		(3,629)
Recoveries on loans previously charged-off		984		813		1,495		4,475
Net recoveries (charge-offs)		(1,937)		(1,329)		(3,628)		846
Provision (release) for loan losses		6,208		7,575		13,310		14,712
Balance at end of period		113,144		96,326		113,144		96,326
Ending balance, loans individually evaluated for impairment		2,889	[1]	11,113	[1]	2,889	[1]	11,113	[1]	11,487
Ending balance, loans collectively evaluated for impairment		110,255		85,213		110,255		85,213
Recorded Investment in Loans: [Abstract]
Recorded Investment in Loans, Ending balance, loans individually evaluated for impairment		62,777	[1]	64,851	[2]	62,777	[1]	64,851	[2]	52,171
Recorded Investment in Loans, Ending balance, loans collectively evaluated for impairment		8,383,448		7,506,435		8,383,448		7,506,435
Total loans		8,446,225		7,571,286		8,446,225		7,571,286
Commercial real estate [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		31,606		37,575		31,838		42,362
Loans charged-off		(98)		(2,082)		(985)		(4,664)
Recoveries on loans previously charged-off		272		1,360		870		2,048
Net recoveries (charge-offs)		174		(722)		(115)		(2,616)
Provision (release) for loan losses		(3,570)		(3,554)		(3,513)		(6,447)
Balance at end of period		28,210		33,299		28,210		33,299
Ending balance, loans individually evaluated for impairment		2,102	[1]	4,879	[1]	2,102	[1]	4,879	[1]	2,441
Ending balance, loans collectively evaluated for impairment		26,108		28,420		26,108		28,420
Recorded Investment in Loans: [Abstract]
Recorded Investment in Loans, Ending balance, loans individually evaluated for impairment		13,441	[1]	23,173	[2]	13,441	[1]	23,173	[2]	19,948
Recorded Investment in Loans, Ending balance, loans collectively evaluated for impairment		2,981,091		2,495,954		2,981,091		2,495,954
Total loans		2,994,532		2,519,127		2,994,532		2,519,127
Construction [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		4,026		3,547		4,290		3,338
Loans charged-off		0		0		0		0
Recoveries on loans previously charged-off		164		9		183		16
Net recoveries (charge-offs)		164		9		183		16
Provision (release) for loan losses		(374)		65		(657)		267
Balance at end of period		3,816		3,621		3,816		3,621
Ending balance, loans individually evaluated for impairment	[1]	0		0		0		0
Ending balance, loans collectively evaluated for impairment		3,816		3,621		3,816		3,621
Recorded Investment in Loans: [Abstract]
Recorded Investment in Loans, Ending balance, loans individually evaluated for impairment		0	[1]	0	[2]	0	[1]	0	[2]
Recorded Investment in Loans, Ending balance, loans collectively evaluated for impairment		371,096		360,313		371,096		360,313
Total loans		371,096		360,313		371,096		360,313
Residential real estate [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		5,223		6,978		5,316		7,555
Loans charged-off		(194)		(180)		(231)		(415)
Recoveries on loans previously charged-off		47		135		104		435
Net recoveries (charge-offs)		(147)		(45)		(127)		20
Provision (release) for loan losses		181		(1,653)		68		(2,295)
Balance at end of period		5,257		5,280		5,257		5,280
Ending balance, loans individually evaluated for impairment		606	[1]	630	[1]	606	[1]	630	[1]	735
Ending balance, loans collectively evaluated for impairment		4,651		4,650		4,651		4,650
Recorded Investment in Loans: [Abstract]
Recorded Investment in Loans, Ending balance, loans individually evaluated for impairment		4,116	[1]	9,337	[2]	4,116	[1]	9,337	[2]	5,274
Recorded Investment in Loans, Ending balance, loans collectively evaluated for impairment		411,710		327,992		411,710		327,992
Total loans		415,826		337,329		415,826		337,329
Home equity [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		4,588		5,500		4,924		5,648
Loans charged-off		0		(268)		(371)		(715)
Recoveries on loans previously charged-off		73		60		143		88
Net recoveries (charge-offs)		73		(208)		(228)		(627)
Provision (release) for loan losses		(46)		(277)		(81)		(6)
Balance at end of period		4,615		5,015		4,615		5,015
Ending balance, loans individually evaluated for impairment		1,865	[1]	1,715	[1]	1,865	[1]	1,715	[1]	1,855
Ending balance, loans collectively evaluated for impairment		2,750		3,300		2,750		3,300
Recorded Investment in Loans: [Abstract]
Recorded Investment in Loans, Ending balance, loans individually evaluated for impairment		12,902	[1]	11,630	[2]	12,902	[1]	11,630	[2]	12,466
Recorded Investment in Loans, Ending balance, loans collectively evaluated for impairment		124,559		132,451		124,559		132,451
Total loans		137,461		144,081		137,461		144,081
Personal [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		2,294		3,088		2,668		3,438
Loans charged-off		(28)		(13)		(38)		(143)
Recoveries on loans previously charged-off		86		20		959		426
Net recoveries (charge-offs)		58		7		921		283
Provision (release) for loan losses		(343)		(145)		(1,580)		(771)
Balance at end of period		2,009		2,950		2,009		2,950
Ending balance, loans individually evaluated for impairment		6	[1]	150	[1]	6	[1]	150	[1]	109
Ending balance, loans collectively evaluated for impairment		2,003		2,800		2,003		2,800
Recorded Investment in Loans: [Abstract]
Recorded Investment in Loans, Ending balance, loans individually evaluated for impairment		24	[1]	580	[2]	24	[1]	580	[2]	$ 430
Recorded Investment in Loans, Ending balance, loans collectively evaluated for impairment		178,117		204,226		178,117		204,226
Total loans		$ 178,141		$ 204,806		$ 178,141		$ 204,806

[1] Refer to Note 4 for additional information regarding impaired loans.

[2] Deposit amounts represent the elimination of Holding Company cash accounts included in total deposits of the Banking segment.