Provision for Income Taxes (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Provision For Income Tax [Line Items]
Tax provision at U.S. Federal statutory rates	35.00%	35.00%
State income taxes net of federal benefit	4.40%	6.00%
Non-deductible permanent items	(9.70%)	6.50%
Non-taxable entities	(1.90%)	(3.20%)
Stock-based compensation	0.90%	0.00%
Other	1.40%	2.50%
Change in valuation allowance	(2.90%)	0.00%
Change in rate	(19.40%)	0.00%
Effective income tax rate	7.80%	46.80%