Loans and Leases and the Allowance for Credit Losses - Interest Income Recognized on Impaired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	$ 800,863	$ 745,805
Interest income recognized, Total	8,917	9,971
Interest income recognized, Cash basis	5,771	7,320
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	225,374	181,846
Interest income recognized, Total	1,091	3,147
Interest income recognized, Cash basis	1,091	3,147
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	265,248	272,172
Interest income recognized, Total	3,038	783
Interest income recognized, Cash basis	3,038	783
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	8,875	9,840
Interest income recognized, Total	115	1,682
Interest income recognized, Cash basis	115	1,682
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	20,398	10,102
Interest income recognized, Total	564	6
Interest income recognized, Cash basis	564	6
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	140,403	121,209
Interest income recognized, Total	2,022	1,902
Interest income recognized, Cash basis	666	902
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	78,238	85,595
Interest income recognized, Total	1,353	1,728
Interest income recognized, Cash basis	208	696
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	47,556	48,797
Interest income recognized, Total	416	414
Interest income recognized, Cash basis	62	86
Recreational Finance [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	6,023	1,458
Interest income recognized, Total	142	63
Interest income recognized, Cash basis	4	2
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	3,530	13,125
Interest income recognized, Total	54	224
Interest income recognized, Cash basis	19	15
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	5,218	1,661
Interest income recognized, Total	122	22
Interest income recognized, Cash basis	$ 4	$ 1