Loans and Leases and the Allowance for Credit Losses - Interest Income Recognized on Impaired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	$ 757,701	$ 799,615
Interest income recognized, Total	6,611	5,772
Interest income recognized, Cash basis	4,009	3,825
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	182,857	182,454
Interest income recognized, Total	975	1,474
Interest income recognized, Cash basis	975	1,474
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	271,825	296,584
Interest income recognized, Total	478	611
Interest income recognized, Cash basis	478	611
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	20,051	33,750
Interest income recognized, Total	429	42
Interest income recognized, Cash basis	429	42
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	16,328	16,868
Interest income recognized, Total	847	38
Interest income recognized, Cash basis	847	38
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	103,875	96,788
Interest income recognized, Total	1,636	1,372
Interest income recognized, Cash basis	774	882
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	97,121	107,473
Interest income recognized, Total	1,500	1,472
Interest income recognized, Cash basis	384	630
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	45,542	26,019
Interest income recognized, Total	399	246
Interest income recognized, Cash basis	100	85
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	16,504	21,962
Interest income recognized, Total	275	339
Interest income recognized, Cash basis	19	36
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	3,598	17,717
Interest income recognized, Total	72	178
Interest income recognized, Cash basis	$ 3	$ 27