Provision for Income Taxes (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Provision For Income Tax [Line Items]
Tax provision at U.S. Federal statutory rates	21.00%	35.00%
State income taxes net of federal benefit	6.70%	4.40%
Non-deductible permanent items	1.30%	(9.70%)
Non-taxable entities	(0.70%)	(1.90%)
Stock-based compensation	(1.80%)	0.90%
Other	0.10%	1.40%
Change in valuation allowance		(2.90%)
Entity Conversion	0.50%	0.00%
Change in rate	0.00%	(19.40%)
Effective income tax rate	27.10%	7.80%