Loans and Leases and the Allowance for Credit Losses - Interest Income Recognized on Impaired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	$ 757,997	$ 754,780	$ 744,561	$ 747,412
Interest income recognized, Total	11,147	7,013	30,818	19,468
Interest income recognized, Cash basis	8,195	4,333	22,055	11,573
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	204,315	233,572	184,795	205,814
Interest income recognized, Total	1,489	1,425	8,447	3,213
Interest income recognized, Cash basis	1,489	1,425	8,447	3,213
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	256,196	224,526	266,594	242,410
Interest income recognized, Total	1,985	391	4,101	1,674
Interest income recognized, Cash basis	1,985	391	4,101	1,674
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	9,000	8,550	9,111	14,551
Interest income recognized, Total		895	1,682	1,791
Interest income recognized, Cash basis		895	1,682	1,791
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	9,623	16,578	9,056	15,474
Interest income recognized, Total	3,379	25	3,438	958
Interest income recognized, Cash basis	3,379	25	3,438	958
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	133,337	113,892	126,910	108,741
Interest income recognized, Total	1,959	1,903	6,190	5,004
Interest income recognized, Cash basis	773	905	2,612	2,285
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	81,729	91,974	83,700	94,680
Interest income recognized, Total	1,607	1,624	4,763	4,573
Interest income recognized, Cash basis	481	569	1,494	1,292
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	48,542	47,831	48,661	46,829
Interest income recognized, Total	421	419	1,268	1,240
Interest income recognized, Cash basis	62	99	220	290
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	7,805	14,588	11,189	15,483
Interest income recognized, Total	181	251	630	788
Interest income recognized, Cash basis	20	22	49	62
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	7,450	3,269	4,545	3,430
Interest income recognized, Total	126	80	299	227
Interest income recognized, Cash basis	$ 6	$ 2	$ 12	$ 8