Loans and Allowance for Loan Losses - Age Analysis of Past Due Loans Segregated by Class of Loans (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	$ 11,270	$ 16,134
60-89 Days Past Due	3,964	2,904
90 Days and Greater	6,294	7,196
Total Past Due Loans	21,528	26,234
Current Loans	3,839,303	3,360,912
Total Loans	3,860,831	3,387,146
Accruing Loans 90 Days or More Past Due	1,135	1,179
Non-residential Real Estate Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	635	411
90 Days and Greater	269	316
Total Past Due Loans	904	727
Current Loans	482,731	454,305
Total Loans	483,635	455,032
Accruing Loans 90 Days or More Past Due	70	96
Non-residential Real Estate Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	377	5,391
60-89 Days Past Due	317	269
90 Days and Greater	825	1,543
Total Past Due Loans	1,519	7,203
Current Loans	952,484	856,179
Total Loans	954,003	863,382
Accruing Loans 90 Days or More Past Due		2
Residential Real Estate Permanent Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	2,010	2,000
60-89 Days Past Due	758	566
90 Days and Greater	544	789
Total Past Due Loans	3,312	3,355
Current Loans	304,267	262,625
Total Loans	307,579	265,980
Accruing Loans 90 Days or More Past Due	172	275
Residential Real Estate All Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,820	2,159
60-89 Days Past Due	194	211
90 Days and Greater	1,488	1,272
Total Past Due Loans	3,502	3,642
Current Loans	633,586	564,231
Total Loans	637,088	567,873
Accruing Loans 90 Days or More Past Due	387	184
Non-consumer Non-real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	841	1,122
60-89 Days Past Due	71	118
90 Days and Greater	793	1,047
Total Past Due Loans	1,705	2,287
Current Loans	965,002	793,028
Total Loans	966,707	795,315
Accruing Loans 90 Days or More Past Due	24	125
Consumer Non-real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,914	1,761
60-89 Days Past Due	711	667
90 Days and Greater	330	392
Total Past Due Loans	2,955	2,820
Current Loans	244,810	225,515
Total Loans	247,765	228,335
Accruing Loans 90 Days or More Past Due	215	279
Other Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,858	1,799
60-89 Days Past Due	916	763
90 Days and Greater	741	1,244
Total Past Due Loans	3,515	3,806
Current Loans	158,902	141,550
Total Loans	162,417	145,356
Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,815	1,491
60-89 Days Past Due	997	310
90 Days and Greater	1,304	593
Total Past Due Loans	4,116	2,394
Current Loans	97,521	63,479
Total Loans	101,637	65,873
Accruing Loans 90 Days or More Past Due	$ 267	$ 218

Financing receivables that are less than 60 days past due but more than 29 days past due.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

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Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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