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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	$ 801,024	$ 729,881	$ 800,947	$ 737,845
Interest income recognized, Total	10,274	9,700	19,191	19,671
Interest income recognized, Cash basis	7,012	6,540	12,783	13,860
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	214,775	168,224	220,075	175,035
Interest income recognized, Total	2,032	3,811	3,123	6,958
Interest income recognized, Cash basis	2,032	3,811	3,123	6,958
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	273,924	271,413	269,586	271,793
Interest income recognized, Total	3,627	1,333	6,665	2,116
Interest income recognized, Cash basis	3,627	1,333	6,665	2,116
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	9,590	8,494	9,233	9,167
Interest income recognized, Total	35		150	1,682
Interest income recognized, Cash basis	35		150	1,682
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	22,521	7,443	21,460	8,773
Interest income recognized, Total	12	53	576	59
Interest income recognized, Cash basis	12	53	576	59
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	142,555	126,185	141,479	123,697
Interest income recognized, Total	2,390	2,329	4,412	4,231
Interest income recognized, Cash basis	1,004	937	1,670	1,839
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	75,940	83,776	77,089	84,686
Interest income recognized, Total	1,452	1,428	2,805	3,156
Interest income recognized, Cash basis	218	317	426	1,013
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	47,435	48,644	47,496	48,721
Interest income recognized, Total	406	433	822	847
Interest income recognized, Cash basis	57	72	119	158
Recreational Finance [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	5,808	1,480	5,917	1,469
Interest income recognized, Total	125	65	267	128
Interest income recognized, Cash basis	4	3	8	5
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	3,450	12,636	3,490	12,881
Interest income recognized, Total	53	225	107	449
Interest income recognized, Cash basis	18	14	37	29
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	5,026	1,586	5,122	1,623
Interest income recognized, Total	142	$ 23	264	45
Interest income recognized, Cash basis	$ 5		$ 9	$ 1