Loans - 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]
Commercial and industrial	$ 4,708,665	$ 4,828,612	$ 4,042,852
Commercial mortgages	2,520,298	2,495,481	2,357,206
Construction	647,862	608,306	493,600
Land	223,349	216,008	184,078
Total commercial real estate	3,391,509	3,319,795	3,034,884
Home equity loans	312,429	310,675	288,961
Home equity lines of credit	188,142	186,522	190,371
1-4 family residential mortgages	36,215	38,323	43,284
Construction	13,170	17,621	18,910
Other	221,700	224,206	219,760
Total consumer real estate	771,656	777,347	761,286
Total real estate	4,163,165	4,097,142	3,796,170
Consumer installment	303,751	311,310	296,057
Other	7,597	8,435	8,415
Total consumer and other	311,348	319,745	304,472
Unearned discounts	(20,827)	(21,651)	(16,781)
Total loans	9,162,351	9,223,848	8,126,713
Total commercial and industrial percentage of total loans	51.40%	52.30%	49.80%
Commercial mortgages percentage of total loans	27.50%	27.10%	29.00%
Construction percentage of total loans	7.10%	6.60%	6.10%
Land percentage of total loans	2.40%	2.30%	2.20%
Total commercial real estate percentage of total loans	37.00%	36.00%	37.30%
Home equity loans percentage of total loans	3.40%	3.40%	3.60%
Home equity lines of credit percentage of total loans	2.10%	2.00%	2.40%
1-4 family residential mortgages percentage of total loans	0.40%	0.40%	0.50%
Construction percentage of total loans	0.10%	0.20%	0.20%
Other percentage of total loans	2.40%	2.40%	2.70%
Total consumer real estate percentage of total loans	8.40%	8.40%	9.40%
Total real estate percentage of total loans	45.40%	44.40%	46.70%
Consumer installment percentage of total loans	3.30%	3.40%	3.60%
Other percentage of total loans	0.10%	0.10%	0.10%
Total consumer and other percentage of total loans	3.40%	3.50%	3.70%
Unearned discounts percentage of total loans	(0.20%)	(0.20%)	(0.20%)
Total loans percentage	100.00%	100.00%	100.00%
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	4,252,568	4,357,100	3,709,450
Total commercial and industrial percentage of total loans	46.40%	47.20%	45.70%
Leases [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	281,106	278,535	193,162
Total commercial and industrial percentage of total loans	3.10%	3.00%	2.40%
Asset-Based [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	$ 174,991	$ 192,977	$ 140,240
Total commercial and industrial percentage of total loans	1.90%	2.10%	1.70%