Loans and Allowance for Loan Losses - Age Analysis of Past Due Loans Segregated by Class of Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	$ 24,673	$ 21,528
Current Loans	4,207,375	3,829,870
Total Loans	4,232,048	3,851,398
Accruing Loans 90 Days or More Past Due	1,841	1,135
30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	16,404	11,270
60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	2,831	3,964
90 Days and Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	5,438	6,294
Non-residential Real Estate Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	803	904
Current Loans	502,094	482,731
Total Loans	502,897	483,635
Accruing Loans 90 Days or More Past Due		70
Non-residential Real Estate Owner Occupied [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	441	635
Non-residential Real Estate Owner Occupied [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	179
Non-residential Real Estate Owner Occupied [Member] | 90 Days and Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	183	269
Non-residential Real Estate Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	1,825	1,519
Current Loans	1,108,935	952,484
Total Loans	1,110,760	954,003
Accruing Loans 90 Days or More Past Due	521
Non-residential Real Estate Other [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	1,149	377
Non-residential Real Estate Other [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	108	317
Non-residential Real Estate Other [Member] | 90 Days and Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	568	825
Residential Real Estate Permanent Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	4,124	3,312
Current Loans	328,477	304,267
Total Loans	332,601	307,579
Accruing Loans 90 Days or More Past Due	493	172
Residential Real Estate Permanent Mortgage [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	2,840	2,010
Residential Real Estate Permanent Mortgage [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	636	758
Residential Real Estate Permanent Mortgage [Member] | 90 Days and Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	648	544
Residential Real Estate All Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	4,275	3,502
Current Loans	672,414	633,586
Total Loans	676,689	637,088
Accruing Loans 90 Days or More Past Due	193	387
Residential Real Estate All Other [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	2,842	1,820
Residential Real Estate All Other [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	609	194
Residential Real Estate All Other [Member] | 90 Days and Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	824	1,488
Non-consumer Non-real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	2,626	1,705
Current Loans	982,136	965,002
Total Loans	984,762	966,707
Accruing Loans 90 Days or More Past Due	152	24
Non-consumer Non-real Estate [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	2,278	841
Non-consumer Non-real Estate [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	161	71
Non-consumer Non-real Estate [Member] | 90 Days and Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	187	793
Consumer Non-real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	3,358	2,955
Current Loans	265,511	244,810
Total Loans	268,869	247,765
Accruing Loans 90 Days or More Past Due	278	215
Consumer Non-real Estate [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	2,237	1,914
Consumer Non-real Estate [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	772	711
Consumer Non-real Estate [Member] | 90 Days and Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	349	330
Other Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	5,621	3,515
Current Loans	156,995	149,469
Total Loans	162,616	152,984
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	3,565	1,858
Other Loans [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	295	916
Other Loans [Member] | 90 Days and Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	1,761	741
Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	2,041	4,116
Current Loans	190,813	97,521
Total Loans	192,854	101,637
Accruing Loans 90 Days or More Past Due	72	267
Acquired Loans [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	1,052	1,815
Acquired Loans [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	71	997
Acquired Loans [Member] | 90 Days and Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	$ 918	$ 1,304