Loans and Allowance for Loan Losses - Age Analysis of Past Due Loans Segregated by Class of Loans (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	$ 17,157		$ 16,633
60-89 Days Past Due	2,433		2,037
90 Days and Greater	6,614		8,368
Total Past Due Loans	26,204		27,038
Current Loans	3,831,538		3,515,232
Total Loans	3,857,742	3,860,831	3,542,270
Accruing Loans 90 Days or More Past Due	1,498	1,135	910
Non-residential Real Estate Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	417		518
90 Days and Greater	258		298
Total Past Due Loans	675		816
Current Loans	486,183		457,978
Total Loans	486,858		458,794
Accruing Loans 90 Days or More Past Due	60		96
Non-residential Real Estate Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	4,597		4,978
90 Days and Greater	825		935
Total Past Due Loans	5,422		5,913
Current Loans	951,760		873,592
Total Loans	957,182		879,505
Residential Real Estate Permanent Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,922		1,391
60-89 Days Past Due	403		476
90 Days and Greater	337		458
Total Past Due Loans	2,662		2,325
Current Loans	310,115		270,879
Total Loans	312,777		273,204
Accruing Loans 90 Days or More Past Due	49		76
Residential Real Estate All Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,732		1,101
60-89 Days Past Due	477		173
90 Days and Greater	1,320		543
Total Past Due Loans	3,529		1,817
Current Loans	636,092		565,930
Total Loans	639,621		567,747
Accruing Loans 90 Days or More Past Due	464		86
Non-consumer Non-real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	3,413		2,599
60-89 Days Past Due	239		150
90 Days and Greater	1,127		929
Total Past Due Loans	4,779		3,678
Current Loans	958,831		824,361
Total Loans	963,610		828,039
Accruing Loans 90 Days or More Past Due	250		18
Consumer Non-real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,678		1,561
60-89 Days Past Due	668		526
90 Days and Greater	272		260
Total Past Due Loans	2,618		2,347
Current Loans	239,584		223,615
Total Loans	242,202		225,962
Accruing Loans 90 Days or More Past Due	201		218
Other Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,373		1,569
60-89 Days Past Due	452
90 Days and Greater	1,075		1,071
Total Past Due Loans	2,900		2,640
Current Loans	162,228		145,571
Total Loans	165,128		148,211
Accruing Loans 90 Days or More Past Due	352
Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	2,025		2,916
60-89 Days Past Due	194		712
90 Days and Greater	1,400		3,874
Total Past Due Loans	3,619		7,502
Current Loans	86,745		153,306
Total Loans	90,364		160,808
Accruing Loans 90 Days or More Past Due	$ 122		$ 416

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

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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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