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Income Taxes - Reconciliation of Effective Tax Rate and Statutory Federal Income Tax Rate (Detail)
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Income Tax Disclosure [Abstract]      
Federal statutory income tax rate 35.00% 35.00% 35.00%
State income taxes, net of federal tax benefit 6.60% 7.00% 6.80%
Tax-exempt interest on municipal obligations (0.70%) (0.40%) (0.40%)
Tax-exempt life insurance related income (1.30%) (1.50%) (1.30%)
Non-deductible joint beneficiary agreement expense 0.10% 0.20% 0.20%
Non-deductible merger expense   1.00%  
Other   0.20% (0.10%)
Effective Tax Rate 39.70% 41.50% 40.20%