Income Taxes - Reconciliation of Effective Tax Rate and Statutory Federal Income Tax Rate (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	35.00%	35.00%	35.00%	35.00%
State income taxes, net of federal tax benefit	6.50%	7.10%	6.70%	7.00%
Tax-exempt interest on municipal obligations	(0.80%)	(0.30%)	(0.60%)	(0.40%)
Increase in cash value of insurance policies	(1.30%)	(1.20%)	(1.40%)	(1.30%)
Nondeductible merger expenses		1.30%		0.90%
Other	0.40%	0.30%	0.20%	0.40%
Effective Tax Rate	39.80%	42.20%	39.90%	41.60%