Income Taxes - Reconciliation of the Federal Statutory Rate (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income tax provision at federal statutory rate	21.00%	21.00%	21.00%
Increase (decrease) in tax resulting from:
State tax provision, net of federal benefit	2.60%	8.30%	6.20%
Foreign tax rate differential	(0.20%)	0.40%	(0.20%)
Stock option compensation	5.70%	(1.20%)	(1.10%)
Withholding taxes	3.30%	(3.50%)	2.10%
Non-deductible expenses	2.20%	(9.80%)	5.30%
Change in valuation allowance	(5.80%)	2.30%
Foreign subsidiary income subject to U.S. tax	(4.30%)	(7.40%)
Change in tax legislation	(0.019)	(0.012)	0.019
Audit settlements		(8.30%)
Other, net	0.20%	(0.30%)	(0.60%)
Effective tax rate	22.80%	0.30%	34.60%