Income Taxes - Income Tax Provision Differences from Expected Statutory Provision (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Expected provision at statutory rate	35.00%	35.00%	35.00%
Difference resulting from:
Tax exempt interest income	(15.60%)	(9.50%)	(11.20%)
Increase in value of bank owned life insurance assets	(4.20%)	(1.20%)	(1.90%)
Stock-based compensation	(1.70%)	0.50%	0.60%
Non-deductible merger-related expenses	1.20%	0.40%	0.80%
State income taxes, net of federal benefits	(1.50%)	0.90%	2.60%
Changes in valuation allowance	3.10%	0.40%	(0.60%)
Other	0.30%	(0.10%)	(0.20%)
Provision for income taxes - effective income tax rate	16.60%	26.40%	25.10%