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Allowance for Loan Losses - Summary of Allowance for Loan Losses and Recorded Investments (Detail) - USD ($) | Jun. 30, 2015 | Mar. 31, 2015 | Dec. 31, 2014 | Jun. 30, 2014 | Mar. 31, 2014 | Dec. 31, 2013
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Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |  |
Allowance for Loan Losses, Individually Evaluated for Impairment | $ 608,000 |  | $ 54,000 |  |  |
Allowance for Loan Losses, Collectively Evaluated for Impairment | 48,206,000 |  | 47,857,000 |  |  |
Total Allowance for Loan Losses | 48,814,000 | $ 48,106,000 | 47,911,000 | $ 46,580,000 | $ 46,616,000 | $ 46,255,000
Portfolio Loans, Individually Evaluated for Impairment | 45,855,000 |  | 43,977,000 |  |  |
Portfolio Loans, Collectively Evaluated for Impairment | 4,752,643,000 |  | 3,824,769,000 |  |  |
Total Portfolio Loans | 4,798,498,000 |  | 3,868,746,000 |  |  |
Commercial Real Estate [Member] |  |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |  |
Allowance for Loan Losses, Individually Evaluated for Impairment | 567,000 |  |  |  |  |
Allowance for Loan Losses, Collectively Evaluated for Impairment | 18,451,000 |  | 20,164,000 |  |  |
Total Allowance for Loan Losses | 19,018,000 | 19,071,000 | 20,164,000 | 20,733,000 | 19,880,000 | 18,921,000
Portfolio Loans, Individually Evaluated for Impairment | 19,297,000 |  | 19,890,000 |  |  |
Portfolio Loans, Collectively Evaluated for Impairment | 2,035,638,000 |  | 1,662,346,000 |  |  |
Total Portfolio Loans | 2,054,935,000 |  | 1,682,236,000 |  |  |
Commercial and Industrial [Member] |  |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |  |
Allowance for Loan Losses, Collectively Evaluated for Impairment | 13,308,000 |  | 13,668,000 |  |  |
Total Allowance for Loan Losses | 13,308,000 | 13,711,000 | 13,668,000 | 13,004,000 | 13,979,000 | 14,433,000
Portfolio Loans, Individually Evaluated for Impairment | 10,125,000 |  | 9,218,000 |  |  |
Portfolio Loans, Collectively Evaluated for Impairment | 1,229,257,000 |  | 984,920,000 |  |  |
Total Portfolio Loans | 1,239,382,000 |  | 994,138,000 |  |  |
Construction Loans [Member] |  |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |  |
Allowance for Loan Losses, Collectively Evaluated for Impairment | 7,671,000 |  | 6,093,000 |  |  |
Total Allowance for Loan Losses | 7,671,000 | 6,869,000 | 6,093,000 | 4,759,000 | 5,183,000 | 5,374,000
Portfolio Loans, Individually Evaluated for Impairment | 9,293,000 |  | 7,605,000 |  |  |
Portfolio Loans, Collectively Evaluated for Impairment | 335,690,000 |  | 208,543,000 |  |  |
Total Portfolio Loans | 344,983,000 |  | 216,148,000 |  |  |
Consumer Real Estate [Member] |  |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |  |
Allowance for Loan Losses, Individually Evaluated for Impairment | 37,000 |  | 43,000 |  |  |
Allowance for Loan Losses, Collectively Evaluated for Impairment | 6,990,000 |  | 6,290,000 |  |  |
Total Allowance for Loan Losses | 7,027,000 | 6,723,000 | 6,333,000 | 6,705,000 | 6,408,000 | 6,362,000
Portfolio Loans, Individually Evaluated for Impairment | 6,944,000 |  | 7,202,000 |  |  |
Portfolio Loans, Collectively Evaluated for Impairment | 1,057,817,000 |  | 903,455,000 |  |  |
Total Portfolio Loans | 1,064,761,000 |  | 910,657,000 |  |  |
Other Consumer [Member] |  |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |  |
Allowance for Loan Losses, Individually Evaluated for Impairment | 4,000 |  | 11,000 |  |  |
Allowance for Loan Losses, Collectively Evaluated for Impairment | 1,786,000 |  | 1,642,000 |  |  |
Total Allowance for Loan Losses | 1,790,000 | $ 1,732,000 | 1,653,000 | $ 1,379,000 | $ 1,166,000 | $ 1,165,000
Portfolio Loans, Individually Evaluated for Impairment | 196,000 |  | 62,000 |  |  |
Portfolio Loans, Collectively Evaluated for Impairment | 94,241,000 |  | 65,505,000 |  |  |
Total Portfolio Loans | 94,437,000 |  | $ 65,567,000 |  |  |
Fair Value Measurements [Member] |  |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |  |
Allowance for loan losses on acquired loans | $ 0 |  |  |  |  |

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- Definition Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Allowance for Loan Losses + References No definition available. + Details
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- Definition The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524 + Details
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- Definition Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524 + Details
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- Definition Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.7(d)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (b)(1)(ii) -URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 6 -Section L -Subsection 1 + Details
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