Summary of Loan Classes and Aging of Past Due Loans (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due and Accruing	$ 36,749	$ 19,871
Greater than 90 Days Past Due and Accruing	5,756	3,554
Non- Accrual Loans	27,580	28,103
Total Past Due	70,085	51,528
Current	5,940,596	5,635,221
Total Loans	6,010,681	5,686,749	5,144,766
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due and Accruing	17,385	5,170
Greater than 90 Days Past Due and Accruing	28	93
Non- Accrual Loans	13,764	14,122
Total Past Due	31,177	19,385
Current	3,155,385	2,854,309
Total Loans	3,186,562	2,873,694
Commercial - credit card [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due and Accruing	2,526	561
Greater than 90 Days Past Due and Accruing	62	43
Non- Accrual Loans	84	61
Total Past Due	2,672	665
Current	115,941	103,655
Total Loans	118,613	104,320
Real estate - construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due and Accruing	25	3,750
Greater than 90 Days Past Due and Accruing
Non- Accrual Loans	1,254	1,263
Total Past Due	1,279	5,013
Current	83,589	73,473
Total Loans	84,868	78,486
Real estate - commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due and Accruing	9,554	3,590
Greater than 90 Days Past Due and Accruing	897	113
Non- Accrual Loans	8,341	8,170
Total Past Due	18,792	11,873
Current	1,424,471	1,423,938
Total Loans	1,443,263	1,435,811
Real estate - residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due and Accruing	1,151	1,371
Greater than 90 Days Past Due and Accruing	548	49
Non- Accrual Loans	777	666
Total Past Due	2,476	2,086
Current	227,016	210,277
Total Loans	229,492	212,363
Real estate - Home Equity Line of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due and Accruing	1,299	1,324
Greater than 90 Days Past Due and Accruing		50
Non- Accrual Loans	259	225
Total Past Due	1,558	1,599
Current	561,207	572,324
Total Loans	562,765	573,923
Consumer - credit card [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due and Accruing	2,740	2,989
Greater than 90 Days Past Due and Accruing	2,668	2,955
Non- Accrual Loans	1,840	2,285
Total Past Due	7,248	8,229
Current	306,899	326,289
Total Loans	314,147	334,518
Consumer - other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due and Accruing	2,069	1,116
Greater than 90 Days Past Due and Accruing	1,553	251
Non- Accrual Loans	1,261	1,311
Total Past Due	4,883	2,678
Current	46,187	51,872
Total Loans	51,070	54,550
Leases [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due and Accruing
Greater than 90 Days Past Due and Accruing
Non- Accrual Loans
Total Past Due
Current	19,901	19,084
Total Loans	$ 19,901	$ 19,084	$ 7,799