Loans and Allowance for Loan Losses - Age Analysis of Past Due Loans Segregated by Class of Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	$ 37,855	$ 24,673
Current Loans	4,269,972	4,207,375
Total Loans	4,307,827	4,232,048
Accruing Loans 90 Days or More Past Due	1,906	1,841
30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	17,537	16,404
60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	5,749	2,831
90 Days and Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	14,569	5,438
Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	5,109	803
Current Loans	521,548	502,094
Total Loans	526,657	502,897
Accruing Loans 90 Days or More Past Due	269
Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	2,585	1,825
Current Loans	1,126,466	1,108,935
Total Loans	1,129,051	1,110,760
Accruing Loans 90 Days or More Past Due	91	521
Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	4,202	4,124
Current Loans	327,619	328,477
Total Loans	331,821	332,601
Accruing Loans 90 Days or More Past Due	468	493
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	3,937	4,275
Current Loans	730,581	672,414
Total Loans	734,518	676,689
Accruing Loans 90 Days or More Past Due	469	193
Real Estate [Member] | 30 to 59 Days Past Due [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	3,899	441
Real Estate [Member] | 30 to 59 Days Past Due [Member] | Non-residential Real Estate Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	504	1,149
Real Estate [Member] | 30 to 59 Days Past Due [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	2,278	2,840
Real Estate [Member] | 30 to 59 Days Past Due [Member] | Residential Real Estate All Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	1,952	2,842
Real Estate [Member] | 60 to 89 Days Past Due [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	704	179
Real Estate [Member] | 60 to 89 Days Past Due [Member] | Non-residential Real Estate Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	86	108
Real Estate [Member] | 60 to 89 Days Past Due [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	895	636
Real Estate [Member] | 60 to 89 Days Past Due [Member] | Residential Real Estate All Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	526	609
Real Estate [Member] | 90 Days and Greater [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	506	183
Real Estate [Member] | 90 Days and Greater [Member] | Non-residential Real Estate Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	1,995	568
Real Estate [Member] | 90 Days and Greater [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	1,029	648
Real Estate [Member] | 90 Days and Greater [Member] | Residential Real Estate All Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	1,459	824
Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	7,190	2,626
Current Loans	989,351	982,136
Total Loans	996,541	984,762
Accruing Loans 90 Days or More Past Due	196	152
Commercial and Financial [Member] | 30 to 59 Days Past Due [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	5,203	2,278
Commercial and Financial [Member] | 60 to 89 Days Past Due [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	1,522	161
Commercial and Financial [Member] | 90 Days and Greater [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	465	187
Consumer Non-real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	3,234	3,358
Current Loans	278,381	265,511
Total Loans	281,615	268,869
Accruing Loans 90 Days or More Past Due	270	278
Consumer Non-real Estate [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	2,020	2,237
Consumer Non-real Estate [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	758	772
Consumer Non-real Estate [Member] | 90 Days and Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	456	349
Other Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	9,642	5,621
Current Loans	138,276	156,995
Total Loans	147,918	162,616
Accruing Loans 90 Days or More Past Due		132
Other Loans [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	1,208	3,565
Other Loans [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	235	295
Other Loans [Member] | 90 Days and Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	8,199	1,761
Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	1,956	2,041
Current Loans	157,750	190,813
Total Loans	159,706	192,854
Accruing Loans 90 Days or More Past Due	143	72
Acquired Loans [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	473	1,052
Acquired Loans [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	1,023	71
Acquired Loans [Member] | 90 Days and Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	$ 460	$ 918