Assumptions for Measuring Fair Values of Stocks (Detail)		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield		0.00%
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate, minimum	[1]	1.40%	2.50%	1.60%
Risk-free interest rate, maximum	[1]	2.50%	3.00%	2.10%
Expected term	[2]	5 years 14 days	5 years 21 days
Expected volatility, minimum	[3]	52.50%	52.40%	54.00%
Expected volatility, maximum	[3]	68.90%	60.80%	63.00%
Stock Options [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	[2]			4 years 9 months 18 days
Stock Options [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	[2]			4 years 2 months 12 days

[1] The risk-free interest rate is estimated using an average of Treasury bill interest rates over a historical period commensurate with the expected term of the option that correlates to the prevailing interest rates at the time of grant.

[2] The expected term is estimated using historical exercise behavior.

[3] The expected volatility is the implied volatility in exchange-traded options of the Company’s common stock.