Annual report pursuant to Section 13 and 15(d)

Income Taxes - Reconciliation between Federal Statutory Income Tax Rate and Effective Tax Rate (Detail)

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Income Taxes - Reconciliation between Federal Statutory Income Tax Rate and Effective 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 taxes, net of federal tax benefits 8.32% 5.86% 4.40%
Tax-exempt municipal securities (0.26%) (0.07%) (0.16%)
Tax credit - federal (2.51%) (2.27%) (1.88%)
Bargain purchase gain 0.00% (7.03%) 0.00%
Other 0.95% (0.01%) (0.99%)
Valuation allowance 0.00% 0.00% 0.00%
Effective tax rate 41.50% 31.48% 36.37%