Loans - Loans (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial:	$ 5,624,833	$ 4,907,076	$ 4,772,617
Commercial mortgages	2,985,184	2,800,760
Construction	577,446	426,639
Land	272,959	239,937
Total commercial real estate	3,835,589	3,467,336	3,371,268
Home equity loans	336,890	329,853
Home equity lines of credit	213,109	195,132
1-4 family residential mortgages	35,625	32,447
Construction	21,506	13,123
Other	256,085	237,649
Total consumer real estate	863,215	808,204	785,205
Total real estate	4,698,804	4,275,540
Consumer installment	371,648	350,827
Other	6,581	7,289
Total consumer and other	378,229	358,116	325,322
Unearned discounts	(22,489)	(25,032)	(21,869)
Total loans	10,679,377	9,515,700	9,232,543
Total commercial and industrial percentage of total loans	52.70%	51.60%
Commercial mortgages percentage of total loans	28.00%	29.40%
Construction percentage of total loans	5.40%	4.50%
Land percentage of total loans	2.50%	2.50%
Total commercial real estate percentage of total loans	35.90%	36.40%
Home equity loans percentage of total loans	3.20%	3.50%
Home equity lines of credit percentage of total loans	2.00%	2.10%
1-4 family residential mortgages percentage of total loans	0.30%	0.30%
Construction percentage of total loans	0.20%	0.10%
Other percentage of total loans	2.40%	2.50%
Total consumer real estate percentage of total loans	8.10%	8.50%
Total real estate percentage of total loans	44.00%	44.90%
Consumer installment percentage of total loans	3.40%	3.70%
Other percentage of total loans	0.10%	0.10%
Total consumer and other percentage of total loans	3.50%	3.80%
Unearned discounts percentage of total loans	(0.20%)	(0.30%)
Total loans percentage	100.00%	100.00%
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial:	5,322,752	4,587,499
Total commercial and industrial percentage of total loans	49.90%	48.20%
Leases [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial:	$ 302,081	$ 319,577
Total commercial and industrial percentage of total loans	2.80%	3.40%