Business Combinations - Additional Information (Detail)
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6 Months Ended |
12 Months Ended |
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Oct. 28, 2015
USD ($)
Branches
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Oct. 03, 2014
USD ($)
$ / shares
shares
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Jun. 30, 2014
USD ($)
Bank
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Dec. 31, 2015
USD ($)
shares
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Dec. 31, 2014
USD ($)
shares
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Aug. 21, 2007
shares
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| Business Acquisition [Line Items] |
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| Business acquisition, common stock issued to acquiree's shareholders | shares |
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6,575,550
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| Fixed share exchange ratio |
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0.9433
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| Aggregate ownership percentage |
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28.90%
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| Cash in-lieu of fractional shares |
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$ 6,823
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| Business combination share outstanding | shares |
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22,775,173
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22,714,964
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15,814,662
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| Assets |
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$ 4,220,722,000
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$ 3,916,458,000
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| Bank Of America [Member] |
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| Business Acquisition [Line Items] |
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| Number of branches | Branches |
3
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| Loans |
$ 400,000
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| Deposits |
$ 235,000,000
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| Percentage of premium on deposits |
1.91%
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| North Valley Bancorp [Member] |
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| Business Acquisition [Line Items] |
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| Loans |
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499,327,000
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| Deposits |
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$ 801,956,000
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| Acquisition, completion date |
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Oct. 03, 2014
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| Closing stock price | $ / shares |
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$ 23.01
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| Consideration paid per share | $ / shares |
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$ 21.71
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| Cash in-lieu of fractional shares |
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$ 7,000
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| Business combination share outstanding | shares |
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22,714,964
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| Business combination consideration value |
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$ 151,310,000
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| Number of commercial banks | Bank |
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22
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| Assets |
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$ 935,000,000
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| Increase in net book value of land and buildings acquired |
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4,785,000
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| Recognized intangible related to acquisition |
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6,614,000
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| North Valley Bancorp [Member] | Junior subordinated debt [Member] |
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| Business Acquisition [Line Items] |
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| Discount on debt instrument |
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$ 6,664,000
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| North Valley Bancorp [Member] | Minimum [Member] | Junior subordinated debt [Member] |
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| Business Acquisition [Line Items] |
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| Amortization period of debt discount |
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18 years
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| North Valley Bancorp [Member] | Maximum [Member] | Junior subordinated debt [Member] |
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| Business Acquisition [Line Items] |
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| Amortization period of debt discount |
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21 years
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| North Valley Bancorp [Member] | Core deposit intangibles [Member] |
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| Business Acquisition [Line Items] |
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| Recognized intangible related to acquisition |
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$ 6,614,000
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| Percentage of acquired intangibles |
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0.97%
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| Finite lived intangible asset useful life |
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7 years
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