Acquisitions (Identifiable Assets and Liabilities Assumed) (Detail) (USD $) In Thousands, unless otherwise specified	1 Months Ended	9 Months Ended
	Feb. 17, 2012	Sep. 30, 2012
Business Acquisition [Line Items]
Value of, Common shares issued and options assumed	$ 302,112	$ 302,112
Value of, Cash	88,005
Total purchase price	390,117
Cash and due from banks	85,518
Unrestricted short-term investments	9,171
Securities available for sale	137,254
Loans and leases	1,975,488	1,975,488
Intangible assets	27,334
Other assets	156,392
Total identifiable assets	2,391,157	2,391,157
Deposits	2,074,372	2,074,372
Short-term borrowings	10,228
Long-term borrowings	103,923
Other liabilities	63,247
Total liabilities	2,251,770	2,251,770
Net goodwill resulting from acquisition	$ 250,730	$ 250,730