Acquisition and Divestiture Activity - Schedule of Preliminary Purchase Price Allocation (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013	Dec. 31, 2012
Business Acquisition [Line Items]
Loans	$ 5,492,716	$ 5,035,819	$ 5,126,904
Deposits	(7,555,003)	(7,210,903)	(6,840,093)
Goodwill	408,474	352,729	339,382	338,820
Tower Financial Corporation [Member]
Business Acquisition [Line Items]
Cash and cash equivalents	56,345
Investment securities	142,759
Loans	371,528
Premises and equipment	8,516
Accrued interest receivable	2,371
Other real estate owned	473
Company-owned life insurance	21,281
Other assets	15,658
Deposits	(527,995)
Short-term borrowings	(18,898)
Other borrowings	(21,113)
Accrued expenses and other liabilities	(4,681)
Net tangible assets acquired	46,244
Definite-lived intangible assets acquired	8,382
Goodwill	55,745
Purchase price	110,371
Bank of America [Member]
Business Acquisition [Line Items]
Cash and cash equivalents	562,906
Loans	5,638
Premises and equipment	12,559
Accrued interest receivable	15
Other assets	331
Deposits	(565,106)
Accrued expenses and other liabilities	(246)
Net tangible assets acquired	16,097
Definite-lived intangible assets acquired	3,462
Goodwill	13,347
Purchase price	$ 32,906