Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2020

Stockholders' Equity and Stock-based Compensation Disclosure [Abstract]

Summary of Activity Related to Stock Option Plans

A summary of the activities related to the Company’s stock option plans is as follows:

			Options Outstanding
	Shares Available for Grant		Number of Shares		Weighted- Average Exercise Price (per share)
Balances as of December 31, 2019	6,111,561		20,859,326		$	124.28
Granted	(581,455	)	581,455		354.55
Exercised	—		(973,969	)	45.77
Expired	—		(48	)	9.96
Balances as of March 31, 2020	5,530,106		20,466,764		$	134.56
Vested and exercisable as of March 31, 2020			20,466,764		$	134.56

Summary of Amounts Related to Option Exercises

A summary of the amounts related to option exercises, is as follows:

	Three Months Ended
	March 31, 2020		March 31, 2019
	(in thousands)
Total intrinsic value of options exercised	$	303,226	$	180,842
Cash received from options exercised	43,694		22,972

Summary of Assumptions Used to Value Stock Option Grants Using Lattice-Binomial Model

The following table summarizes the assumptions used to value option grants using the lattice-binomial model and the valuation data:

	Three Months Ended
	March 31, 2020			March 31, 2019
Dividend yield	—		%	—		%
Expected volatility	37		%	41		%
Risk-free interest rate	1.71		%	2.74		%
Suboptimal exercise factor	3.34			3.07
Weighted-average fair value (per share)	$	167		$	163
Total stock-based compensation expense (in thousands)	$	97,019		$	101,200
Total income tax impact on provision (in thousands)	$	21,309		$	21,628