Summary of Loan Classes and Aging of Past Due Loans (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due and Accruing	$ 27,308	$ 13,330
Greater than 90 Days Past Due and Accruing	4,160	5,998
Non- Accrual Loans	27,389	25,581
Total Past Due	58,857	44,909
Current	5,330,906	4,915,434
Total Loans	5,389,763	4,960,343	4,776,071
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due and Accruing	11,353	2,986
Greater than 90 Days Past Due and Accruing	646	767
Non- Accrual Loans	11,587	9,234
Total Past Due	23,586	12,987
Current	2,667,654	2,221,830
Total Loans	2,691,240	2,234,817
Commercial - credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due and Accruing	805	896
Greater than 90 Days Past Due and Accruing	238	284
Total Past Due	1,043	1,180
Current	108,246	94,159
Total Loans	109,289	95,339
Real estate - construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due and Accruing	732	430
Greater than 90 Days Past Due and Accruing	206
Non- Accrual Loans	1,034	642
Total Past Due	1,972	1,072
Current	71,419	83,518
Total Loans	73,391	84,590
Real estate - commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due and Accruing	6,528	2,368
Greater than 90 Days Past Due and Accruing	344	313
Non- Accrual Loans	8,906	7,218
Total Past Due	15,778	9,899
Current	1,326,358	1,384,656
Total Loans	1,342,136	1,394,555
Real estate - residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due and Accruing	1,533	1,713
Greater than 90 Days Past Due and Accruing	40	247
Non- Accrual Loans	1,183	1,660
Total Past Due	2,756	3,620
Current	201,197	182,266
Total Loans	203,953	185,886
Real estate - HELOC
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due and Accruing	1,410	819
Greater than 90 Days Past Due and Accruing	47	41
Non- Accrual Loans	284	696
Total Past Due	1,741	1,556
Current	562,739	531,476
Total Loans	564,480	533,032
Consumer - credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due and Accruing	3,214	2,858
Greater than 90 Days Past Due and Accruing	2,437	3,394
Non- Accrual Loans	2,999	4,638
Total Past Due	8,650	10,890
Current	314,599	322,756
Total Loans	323,249	333,646
Consumer - other
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due and Accruing	1,733	1,260
Greater than 90 Days Past Due and Accruing	202	952
Non- Accrual Loans	1,396	1,493
Total Past Due	3,331	3,705
Current	59,910	90,939
Total Loans	63,241	94,644
Leases
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	18,784	3,834
Total Loans	$ 18,784	$ 3,834	$ 4,295