Income Taxes - Reconciliation of Effective Tax Rate and Statutory Federal Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	35.00%	35.00%	35.00%
State income taxes, net of federal tax benefit	6.80%	6.60%	7.00%
Tax-exempt interest on municipal obligations	(1.80%)	(0.70%)	(0.40%)
Tax-exempt life insurance related income	(1.30%)	(1.30%)	(1.50%)
Low income housing tax credit benefits	(1.30%)	(0.40%)
Low income housing tax credit amortization	0.80%
Non-deductible joint beneficiary agreement expense	0.10%	0.10%	0.20%
Non-deductible merger expense			1.00%
Other	(0.10%)	0.40%	0.20%
Effective Tax Rate	38.20%	39.70%	41.50%