Loans and Allowance for Loan Losses - Internal Loan Grading by Class of Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	$ 3,959,669	$ 3,851,398
Non-residential Real Estate Owner Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	493,278	483,635
Non-residential Real Estate Other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	1,037,239	954,003
Residential Real Estate Permanent Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	325,137	307,579
Residential Real Estate All Other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	663,035	637,088
Non-consumer Non-real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	934,402	966,707
Consumer Non-real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	268,368	247,765
Other Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	161,326	152,984
Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	76,884	101,637
Grade 1 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	3,349,050	3,248,622
Grade 1 [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	408,259	402,706
Grade 1 [Member] | Non-residential Real Estate Other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	872,939	795,209
Grade 1 [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	288,436	272,411
Grade 1 [Member] | Residential Real Estate All Other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	544,388	529,555
Grade 1 [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	775,900	821,094
Grade 1 [Member] | Consumer Non-real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	252,581	233,424
Grade 1 [Member] | Other Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	153,197	147,758
Grade 1 [Member] | Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	53,350	46,465
Grade 2 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	505,758	507,064
Grade 2 [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	78,173	75,555
Grade 2 [Member] | Non-residential Real Estate Other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	129,399	133,542
Grade 2 [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	29,520	27,855
Grade 2 [Member] | Residential Real Estate All Other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	106,840	99,214
Grade 2 [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	133,200	117,457
Grade 2 [Member] | Consumer Non-real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	13,583	12,229
Grade 2 [Member] | Other Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	4,696	4,261
Grade 2 [Member] | Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	10,347	36,951
Grade 3 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	76,527	78,999
Grade 3 [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	6,663	5,008
Grade 3 [Member] | Non-residential Real Estate Other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	30,023	20,126
Grade 3 [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	6,393	6,369
Grade 3 [Member] | Residential Real Estate All Other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	10,200	6,146
Grade 3 [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	11,804	26,550
Grade 3 [Member] | Consumer Non-real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	1,690	1,548
Grade 3 [Member] | Other Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	1,027	601
Grade 3 [Member] | Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	8,727	12,651
Grade 4 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	28,183	16,158
Grade 4 [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	183	366
Grade 4 [Member] | Non-residential Real Estate Other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	4,878	5,126
Grade 4 [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	788	944
Grade 4 [Member] | Residential Real Estate All Other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	1,607	2,173
Grade 4 [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	13,498	1,606
Grade 4 [Member] | Consumer Non-real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	512	564
Grade 4 [Member] | Other Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	2,406	173
Grade 4 [Member] | Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	4,311	5,206
Grade 5 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	151	555
Grade 5 [Member] | Consumer Non-real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	2
Grade 5 [Member] | Other Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans		191
Grade 5 [Member] | Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	$ 149	$ 364