Loans and Leases and the Allowance for Credit Losses - Interest Income Recognized on Impaired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	$ 729,881	$ 729,652	$ 737,845	$ 743,728
Interest income recognized, Total	9,700	5,844	19,671	12,455
Interest income recognized, Cash basis	6,540	3,231	13,860	7,240
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	168,224	200,005	175,035	191,935
Interest income recognized, Total	3,811	813	6,958	1,788
Interest income recognized, Cash basis	3,811	813	6,958	1,788
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	271,413	230,767	271,793	251,352
Interest income recognized, Total	1,333	805	2,116	1,283
Interest income recognized, Cash basis	1,333	805	2,116	1,283
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	8,494	15,577	9,167	17,552
Interest income recognized, Total		467	1,682	896
Interest income recognized, Cash basis		467	1,682	896
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	7,443	14,213	8,773	14,922
Interest income recognized, Total	53	86	59	933
Interest income recognized, Cash basis	53	86	59	933
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	126,185	108,036	123,697	106,166
Interest income recognized, Total	2,329	1,465	4,231	3,101
Interest income recognized, Cash basis	937	606	1,839	1,380
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	83,776	95,208	84,686	96,033
Interest income recognized, Total	1,428	1,449	3,156	2,949
Interest income recognized, Cash basis	317	339	1,013	723
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	48,644	46,872	48,721	46,327
Interest income recognized, Total	433	422	847	821
Interest income recognized, Cash basis	72	91	158	191
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	12,636	15,506	12,881	15,931
Interest income recognized, Total	225	262	449	537
Interest income recognized, Cash basis	14	21	29	40
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	3,066	3,468	3,092	3,510
Interest income recognized, Total	88	75	173	147
Interest income recognized, Cash basis	$ 3	$ 3	$ 6	$ 6