Loans and Leases and Other Real Estate - Impaired Loans with and without Specific Allowances (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Impaired [Line Items]
Recorded Investment in Impaired Loans	$ 19,702	$ 22,591	$ 25,285
Contractual Unpaid Principal Balance	21,360	23,461	27,356
Loans with related allowance, Related Allowance	338	505
Related Allowance	338	505	529
Interest Income Recognized	592	705	648
Average Investment in Impaired Loans	20,012	23,236	26,675
Commercial, secured by real estate
Financing Receivable, Impaired [Line Items]
Loans without related allowance, Recorded Investment in Impaired Loans	9,284	12,155	12,764
Loans with related allowance, Recorded Investment in Impaired Loans	7,270	5,381	5,860
Recorded Investment in Impaired Loans	16,554	17,536	18,624
Loans without related allowance, Contractual Unpaid Principal Balance	9,829	12,497	13,195
Loans with related allowance, Contractual Unpaid Principal Balance	7,597	5,721	6,142
Contractual Unpaid Principal Balance	17,426	18,218	19,337
Loans with related allowance, Related Allowance	307	454	392
Related Allowance	307	454	392
Loans without related allowance, Interest Income Recognized	188	366	229
Loans with related allowance, Interest Income Recognized	317	206	273
Interest Income Recognized	505	572	502
Loans without related allowance, Average Investment in Impaired Loans	7,369	12,774	13,631
Loans with related allowance, Average Investment in Impaired Loans	7,594	5,029	6,549
Average Investment in Impaired Loans	14,963	17,803	20,180
Commercial, industrial and other
Financing Receivable, Impaired [Line Items]
Loans without related allowance, Recorded Investment in Impaired Loans	1,151	618	603
Loans with related allowance, Recorded Investment in Impaired Loans	209	164	349
Recorded Investment in Impaired Loans	1,360	782	952
Loans without related allowance, Contractual Unpaid Principal Balance	1,449	618	603
Loans with related allowance, Contractual Unpaid Principal Balance	209	164	349
Contractual Unpaid Principal Balance	1,658	782	952
Loans with related allowance, Related Allowance	7	9	12
Related Allowance	7	9	12
Loans without related allowance, Interest Income Recognized	19	25	24
Loans with related allowance, Interest Income Recognized	12	14	17
Interest Income Recognized	31	39	41
Loans without related allowance, Average Investment in Impaired Loans	1,834	618	1,109
Loans with related allowance, Average Investment in Impaired Loans	209	283	360
Average Investment in Impaired Loans	2,043	901	1,469
Leases
Financing Receivable, Impaired [Line Items]
Loans without related allowance, Recorded Investment in Impaired Loans	301	0	0
Loans with related allowance, Recorded Investment in Impaired Loans	30	65	0
Recorded Investment in Impaired Loans	331	65	0
Loans without related allowance, Contractual Unpaid Principal Balance	597	0	0
Loans with related allowance, Contractual Unpaid Principal Balance	30	65	0
Contractual Unpaid Principal Balance	627	65	0
Loans with related allowance, Related Allowance	14	30	0
Related Allowance	14	30	0
Loans without related allowance, Interest Income Recognized	0	0	0
Loans with related allowance, Interest Income Recognized	0	0	0
Interest Income Recognized	0	0	0
Loans without related allowance, Average Investment in Impaired Loans	376	0	0
Loans with related allowance, Average Investment in Impaired Loans	19	29	1
Average Investment in Impaired Loans	395	29	1
Real estate - residential mortgage
Financing Receivable, Impaired [Line Items]
Loans without related allowance, Recorded Investment in Impaired Loans	0	963	1,880
Loans with related allowance, Recorded Investment in Impaired Loans	730	781	1,031
Recorded Investment in Impaired Loans	730	1,744	2,911
Loans without related allowance, Contractual Unpaid Principal Balance	0	980	3,146
Loans with related allowance, Contractual Unpaid Principal Balance	884	919	1,100
Contractual Unpaid Principal Balance	884	1,899	4,246
Loans with related allowance, Related Allowance	4	4	31
Related Allowance	4	4	31
Loans without related allowance, Interest Income Recognized	4	15	16
Loans with related allowance, Interest Income Recognized	20	27	30
Interest Income Recognized	24	42	46
Loans without related allowance, Average Investment in Impaired Loans	242	996	2,430
Loans with related allowance, Average Investment in Impaired Loans	745	940	1,011
Average Investment in Impaired Loans	987	1,936	3,441
Real estate - construction
Financing Receivable, Impaired [Line Items]
Loans without related allowance, Recorded Investment in Impaired Loans	0	1,471	1,471
Loans with related allowance, Recorded Investment in Impaired Loans	0	0	0
Recorded Investment in Impaired Loans	0	1,471	1,471
Loans without related allowance, Contractual Unpaid Principal Balance	0	1,471	1,471
Loans with related allowance, Contractual Unpaid Principal Balance	0	0	0
Contractual Unpaid Principal Balance	0	1,471	1,471
Loans with related allowance, Related Allowance	0	0	0
Related Allowance	0	0	0
Loans without related allowance, Interest Income Recognized	0	0	0
Loans with related allowance, Interest Income Recognized	0	0	0
Interest Income Recognized	0	0	0
Loans without related allowance, Average Investment in Impaired Loans	726	1,471	12
Loans with related allowance, Average Investment in Impaired Loans	0	0	0
Average Investment in Impaired Loans	726	1,471	12
Home equity and consumer
Financing Receivable, Impaired [Line Items]
Loans without related allowance, Recorded Investment in Impaired Loans	0	0	139
Loans with related allowance, Recorded Investment in Impaired Loans	727	993	1,188
Recorded Investment in Impaired Loans	727	993	1,327
Loans without related allowance, Contractual Unpaid Principal Balance	0	0	139
Loans with related allowance, Contractual Unpaid Principal Balance	765	1,026	1,211
Contractual Unpaid Principal Balance	765	1,026	1,350
Loans with related allowance, Related Allowance	6	8	94
Related Allowance	6	8	94
Loans without related allowance, Interest Income Recognized	0	0	0
Loans with related allowance, Interest Income Recognized	32	52	59
Interest Income Recognized	32	52	59
Loans without related allowance, Average Investment in Impaired Loans	0	6	388
Loans with related allowance, Average Investment in Impaired Loans	898	1,090	1,184
Average Investment in Impaired Loans	$ 898	$ 1,096	$ 1,572