Reconciliation of Statutory U.S. Federal Rate and Tax Effective Rates (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Statutory federal income tax rate	21.00%	21.00%	21.00%	35.00%
State income tax, net of federal benefit	3.90%	3.50%	3.40%
State credit carryforwards	0.50%	1.30%	0.30%
U.S. federal R&D tax credit	(1.90%)	(1.90%)	(1.70%)
Tax Reform			(0.10%)
Excess benefit of equity compensation	(3.40%)	(0.10%)	(0.60%)
Employee compensation limitation	2.70%	2.10%	0.90%
Global Intangible Low Taxed Income (GILTI)	0.10%
Foreign-derived intangible income (FDII) deduction	(2.70%)	(3.10%)	(1.60%)
Foreign operations	1.00%	1.10%	1.20%
Tax contingencies	1.90%	3.70%	0.50%
Other permanent differences	(0.20%)	(0.60%)	0.10%
Change in valuation allowance	0.40%	(0.90%)	(0.20%)
Income taxes	23.30%	26.10%	23.20%