Allowance for Loan Losses - Summary of Allowance for Loan Losses and Recorded Investments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	$ 55		$ 97
Allowance for Loan Losses, Collectively Evaluated for Impairment	47,261		46,158
Total Allowance for Loan Losses	47,316	46,580	46,255	47,983	46,105	46,484
Portfolio Loans, Individually Evaluated for Impairment	45,992		52,856
Portfolio Loans, Collectively Evaluated for Impairment	3,755,197		3,513,343
Total Portfolio Loans	3,801,189		3,566,199
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	0		0
Allowance for Loan Losses, Collectively Evaluated for Impairment	19,977		18,921
Total Allowance for Loan Losses	19,977	20,733	18,921	17,689	23,484	25,246
Portfolio Loans, Individually Evaluated for Impairment	21,028		26,968
Portfolio Loans, Collectively Evaluated for Impairment	1,670,621		1,580,788
Total Portfolio Loans	1,691,649		1,607,756
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	0		0
Allowance for Loan Losses, Collectively Evaluated for Impairment	13,898		14,433
Total Allowance for Loan Losses	13,898	13,004	14,433	14,799	9,123	7,759
Portfolio Loans, Individually Evaluated for Impairment	9,643		9,580
Portfolio Loans, Collectively Evaluated for Impairment	936,723		832,869
Total Portfolio Loans	946,366		842,449
Commercial Construction [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	0		25
Allowance for Loan Losses, Collectively Evaluated for Impairment	5,178		5,349
Total Allowance for Loan Losses	5,178	4,759	5,374	7,999	5,812	7,500
Portfolio Loans, Individually Evaluated for Impairment	8,143		8,072
Portfolio Loans, Collectively Evaluated for Impairment	175,366		135,603
Total Portfolio Loans	183,509		143,675
Consumer Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	45		53
Allowance for Loan Losses, Collectively Evaluated for Impairment	6,718		6,309
Total Allowance for Loan Losses	6,763	6,705	6,362	6,377	6,655	5,058
Portfolio Loans, Individually Evaluated for Impairment	7,045		8,079
Portfolio Loans, Collectively Evaluated for Impairment	906,013		896,357
Total Portfolio Loans	913,058		904,436
Other Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	10		19
Allowance for Loan Losses, Collectively Evaluated for Impairment	1,490		1,146
Total Allowance for Loan Losses	1,500	1,379	1,165	1,119	1,031	921
Portfolio Loans, Individually Evaluated for Impairment	133		157
Portfolio Loans, Collectively Evaluated for Impairment	66,474		67,726
Total Portfolio Loans	$ 66,607		$ 67,883