Loans - Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Related Allowance	$ 37,066	$ 45,203
Recorded Investment With Related Allowance	171,601	161,531
Total Recorded Investment	208,667	206,734
Unpaid Contractual Principal Balance	246,695	239,964
Related Allowance	28,150	31,013
Commercial real estate loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Related Allowance	24,349	33,063
Recorded Investment With Related Allowance	106,617	98,153
Total Recorded Investment	130,966	131,216
Unpaid Contractual Principal Balance	148,532	149,553
Related Allowance	14,478	16,581
Consumer loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Related Allowance	992	672
Recorded Investment With Related Allowance	252	258
Total Recorded Investment	1,244	930
Unpaid Contractual Principal Balance	1,587	1,169
Related Allowance	16	15
Commercial and industrial [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Related Allowance	2,308	3,236
Recorded Investment With Related Allowance	46,325	46,461
Total Recorded Investment	48,633	49,697
Unpaid Contractual Principal Balance	66,294	62,183
Related Allowance	9,759	12,088
Commercial real estate [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Related Allowance	18,475	26,724
Recorded Investment With Related Allowance	94,195	84,151
Total Recorded Investment	112,670	110,875
Unpaid Contractual Principal Balance	128,450	125,875
Related Allowance	12,726	11,788
Construction [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Related Allowance	5,874	6,339
Recorded Investment With Related Allowance	12,422	14,002
Total Recorded Investment	18,296	20,341
Unpaid Contractual Principal Balance	20,082	23,678
Related Allowance	1,752	4,793
Residential mortgage [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Related Allowance	9,417	8,232
Recorded Investment With Related Allowance	18,407	16,659
Total Recorded Investment	27,824	24,891
Unpaid Contractual Principal Balance	30,282	27,059
Related Allowance	3,897	2,329
Home equity [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Related Allowance	992	672
Recorded Investment With Related Allowance	252	258
Total Recorded Investment	1,244	930
Unpaid Contractual Principal Balance	1,587	1,169
Related Allowance	$ 16	$ 15