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Stockholders' Equity (Tables)
 6 Months Ended
Jun. 30, 2021
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, 202021,702,085 18,676,810 $170.23 
Granted
(821,692)821,692 526.12
Exercised
— (702,192)92.19 
Expired
— (5,236)30.82 
Balances as of June 30, 202120,880,393 18,791,074 $188.75 
Vested and exercisable as of June 30, 202118,791,074 $188.75 
Summary of Amounts Related to Option Exercises
A summary of the amounts related to option exercises, is as follows:
Three Months EndedSix Months Ended
June 30,
2021		June 30,
2020		June 30,
2021		June 30,
2020
(in thousands)
Total intrinsic value of options exercised$90,290 $442,156 $318,310 $745,382 
Cash received from options exercised19,749 89,060 67,820 132,754 
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 EndedSix Months Ended
June 30,
2021		June 30,
2020		June 30,
2021		June 30,
2020
Dividend yield— %— %— %— %
Expected volatility36 %44 %
36% - 41%
37% - 44%
Risk-free interest rate1.62 %0.74 %
1.08% - 1.62%
0.74% - 1.71%
Suboptimal exercise factor3.82 3.51 
3.81 - 3.82
3.34 - 3.51
Weighted-average fair value (per share)$241 $203 $254 $184 
Total stock-based compensation expense (in thousands)$101,583 $104,210 $208,813 $201,229 
Total income tax impact on provision (in thousands)$22,832 $22,834 $46,911 $44,143