Allowance for Loan Losses - Aging Analysis of Recorded Investment for Loans by Portfolio and Segment (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	$ 289	$ 1,454
Financing receivables past due	473	12,406
Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	14,013	13,740
Financing receivables past due	15,407	16,665
30 to 59 Days Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	33	9,970
30 to 59 Days Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	1,394	2,036
60 to 89 Days Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	151	982
60 to 89 Days Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	889
90 Days or More Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
90 Days or More Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Total real estate loans | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	289	1,454
Financing receivables past due	473	12,406
Total real estate loans | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	13,136	12,840
Financing receivables past due	14,530	15,675
Total real estate loans | 30 to 59 Days Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	33	9,970
Total real estate loans | 30 to 59 Days Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	1,394	1,946
Total real estate loans | 60 to 89 Days Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	151	982
Total real estate loans | 60 to 89 Days Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	889
Total real estate loans | 90 Days or More Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Total real estate loans | 90 Days or More Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Commercial real estate | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	0	0
Financing receivables past due	0	0
Commercial real estate | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	5,171	5,282
Financing receivables past due	5,171	5,345
Commercial real estate | 30 to 59 Days Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Commercial real estate | 30 to 59 Days Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	63
Commercial real estate | 60 to 89 Days Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Commercial real estate | 60 to 89 Days Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Commercial real estate | 90 Days or More Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Commercial real estate | 90 Days or More Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Owner-occupied commercial real estate | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	0	0
Financing receivables past due	33	113
Owner-occupied commercial real estate | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	2,220	2,247
Financing receivables past due	2,755	2,342
Owner-occupied commercial real estate | 30 to 59 Days Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	33	0
Owner-occupied commercial real estate | 30 to 59 Days Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	535	0
Owner-occupied commercial real estate | 60 to 89 Days Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	113
Owner-occupied commercial real estate | 60 to 89 Days Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	95
Owner-occupied commercial real estate | 90 Days or More Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Owner-occupied commercial real estate | 90 Days or More Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
1-4 single family residential | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	289	1,454
Financing receivables past due	440	11,762
1-4 single family residential | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	3,371	3,016
Financing receivables past due	3,495	5,106
1-4 single family residential | 30 to 59 Days Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	9,439
1-4 single family residential | 30 to 59 Days Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	124	1,393
1-4 single family residential | 60 to 89 Days Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	151	869
1-4 single family residential | 60 to 89 Days Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	697
1-4 single family residential | 90 Days or More Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
1-4 single family residential | 90 Days or More Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Construction, land and development | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	0	0
Financing receivables past due	0	467
Construction, land and development | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	0	0
Financing receivables past due	0	0
Construction, land and development | 30 to 59 Days Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	467
Construction, land and development | 30 to 59 Days Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Construction, land and development | 60 to 89 Days Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Construction, land and development | 60 to 89 Days Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Construction, land and development | 90 Days or More Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Construction, land and development | 90 Days or More Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Home equity loans and lines of credit | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	0	0
Financing receivables past due	0	64
Home equity loans and lines of credit | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	2,374	2,295
Financing receivables past due	3,109	2,882
Home equity loans and lines of credit | 30 to 59 Days Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	64
Home equity loans and lines of credit | 30 to 59 Days Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	735	490
Home equity loans and lines of credit | 60 to 89 Days Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Home equity loans and lines of credit | 60 to 89 Days Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	97
Home equity loans and lines of credit | 90 Days or More Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Home equity loans and lines of credit | 90 Days or More Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Total other loans | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	0	0
Financing receivables past due	0	0
Total other loans | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	877	900
Financing receivables past due	877	990
Total other loans | 30 to 59 Days Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Total other loans | 30 to 59 Days Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	90
Total other loans | 60 to 89 Days Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Total other loans | 60 to 89 Days Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Total other loans | 90 Days or More Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Total other loans | 90 Days or More Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Commercial and industrial | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	0	0
Financing receivables past due	0	0
Commercial and industrial | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	877	877
Financing receivables past due	877	967
Commercial and industrial | 30 to 59 Days Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Commercial and industrial | 30 to 59 Days Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	90
Commercial and industrial | 60 to 89 Days Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Commercial and industrial | 60 to 89 Days Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Commercial and industrial | 90 Days or More Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Commercial and industrial | 90 Days or More Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Consumer | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	0	0
Financing receivables past due	0	0
Consumer | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	0	23
Financing receivables past due	0	23
Consumer | 30 to 59 Days Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Consumer | 30 to 59 Days Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Consumer | 60 to 89 Days Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Consumer | 60 to 89 Days Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Consumer | 90 Days or More Past Due | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	0	0
Consumer | 90 Days or More Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivables past due	$ 0	$ 0