Loans and Allowance for Loan Losses - Age Analysis of Past Due Loans Segregated by Class of Loans (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	$ 16,535		$ 14,462
90 Days and Greater	7,099		6,468
Total Past Due Loans	23,634		20,930
Current Loans	3,335,304		3,095,166
Total Loans	3,358,938	3,242,427	3,116,096
Accruing Loans 90 Days or More Past Due	1,266	537	731
Non-residential real estate owner occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	779		915
90 Days and Greater	326		466
Total Past Due Loans	1,105		1,381
Current Loans	458,241		480,319
Total Loans	459,346		481,700
Accruing Loans 90 Days or More Past Due	308		349
Non-residential real estate other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	6,046		646
90 Days and Greater	1,925		1,959
Total Past Due Loans	7,971		2,605
Current Loans	869,531		665,265
Total Loans	877,502		667,870
Accruing Loans 90 Days or More Past Due	51
Residential real estate permanent mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	2,017		2,058
90 Days and Greater	492		399
Total Past Due Loans	2,509		2,457
Current Loans	253,708		242,209
Total Loans	256,217		244,666
Accruing Loans 90 Days or More Past Due	217		12
Residential real estate all other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	1,900		1,635
90 Days and Greater	1,401		771
Total Past Due Loans	3,301		2,406
Current Loans	547,849		490,726
Total Loans	551,150		493,132
Accruing Loans 90 Days or More Past Due	32		86
Non-consumer non-real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	889		4,233
90 Days and Greater	1,013		135
Total Past Due Loans	1,902		4,368
Current Loans	776,576		729,538
Total Loans	778,478		733,906
Accruing Loans 90 Days or More Past Due	138		7
Consumer non-real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	2,179		2,050
90 Days and Greater	194		230
Total Past Due Loans	2,373		2,280
Current Loans	222,122		205,463
Total Loans	224,495		207,743
Accruing Loans 90 Days or More Past Due	187		170
Other loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	1,531		1,706
90 Days and Greater	1,275		1,447
Total Past Due Loans	2,806		3,153
Current Loans	136,060		147,329
Total Loans	138,866		150,482
Accruing Loans 90 Days or More Past Due	236		43
Acquired loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	1,194		1,219
90 Days and Greater	473		1,061
Total Past Due Loans	1,667		2,280
Current Loans	71,217		134,317
Total Loans	72,884		136,597
Accruing Loans 90 Days or More Past Due	$ 97		$ 64