Loans and Allowance for Loan Losses - Age Analysis of Past Due Loans Segregated by Class of Loans (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	$ 18,827		$ 13,194
90 Days and Greater	9,280		7,153
Total Past Due Loans	28,107		20,347
Current Loans	3,637,801		3,224,737
Total Loans	3,665,908	3,387,146	3,245,084
Accruing Loans 90 Days or More Past Due	1,789	1,179	850
Non-residential real estate owner occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	477		1,848
90 Days and Greater	264		138
Total Past Due Loans	741		1,986
Current Loans	482,081		444,231
Total Loans	482,822		446,217
Accruing Loans 90 Days or More Past Due	60		120
Non-residential real estate other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	5,065		230
90 Days and Greater	825		3,056
Total Past Due Loans	5,890		3,286
Current Loans	920,264		801,821
Total Loans	926,154		805,107
Accruing Loans 90 Days or More Past Due	0		51
Residential real estate permanent mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	2,224		1,496
90 Days and Greater	656		566
Total Past Due Loans	2,880		2,062
Current Loans	282,749		249,671
Total Loans	285,629		251,733
Accruing Loans 90 Days or More Past Due	180		102
Residential real estate all other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	1,545		1,494
90 Days and Greater	892		251
Total Past Due Loans	2,437		1,745
Current Loans	598,454		539,276
Total Loans	600,891		541,021
Accruing Loans 90 Days or More Past Due	538		49
Non-consumer non-real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	2,059		3,519
90 Days and Greater	985		816
Total Past Due Loans	3,044		4,335
Current Loans	859,012		745,327
Total Loans	862,056		749,662
Accruing Loans 90 Days or More Past Due	46		32
Consumer non-real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	2,256		2,382
90 Days and Greater	313		213
Total Past Due Loans	2,569		2,595
Current Loans	230,774		214,785
Total Loans	233,343		217,380
Accruing Loans 90 Days or More Past Due	219		176
Other loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	1,695		1,850
90 Days and Greater	356		1,520
Total Past Due Loans	2,051		3,370
Current Loans	146,218		144,135
Total Loans	148,269		147,505
Accruing Loans 90 Days or More Past Due	0		0
Acquired loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	3,506		375
90 Days and Greater	4,989		593
Total Past Due Loans	8,495		968
Current Loans	118,249		85,491
Total Loans	126,744		86,459
Accruing Loans 90 Days or More Past Due	$ 746		$ 320