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Stock-Based Compensation (Tables) | 9 Months Ended
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Sep. 30, 2021
Share-based Payment Arrangement [Abstract] |
Summary of Expense Related to Share-Based Payments | The table below summarizes the expense related to share-based payments recognized in the three and nine months ended September 30 (in thousands):
|  | Three Months Ended September 30, |  | Nine Months Ended September 30,
|  | 2021 |  | 2020 |  | 2021 |  | 2020
Stock options |  | $ | 3,792 |  |  | $ | 5,294 |  |  | $ | 13,394 |  |  | $ | 18,069 |
Restricted stock |  | 12,661 |  |  | 6,610 |  |  | 38,691 |  |  | 16,999 |
Stock-based compensation |  | $ | 16,453 |  |  | $ | 11,904 |  |  | $ | 52,085 |  |  | $ | 35,069 |
Summary of Total Unrecognized Compensation Cost Related to Stock-Based Compensation | The following table summarizes the Company’s total unrecognized compensation cost related to stock-based compensation as of September 30, 2021 (cost in thousands):
|  | Unrecognized Compensation Cost |  | Weighted Average Period of Expense Recognition (in Years)
Stock options |  | $ | 95,662 |  |  | 1.79
Restricted stock |  | 40,650 |  |  | 0.94
Total |  | $ | 136,312 |  |  |
Summary of Changes in Number of Shares of Common Stock Under Option | The following summarizes the changes in the number of shares of common stock under option for the nine months ended September 30, 2021 (shares/options and aggregate intrinsic value in thousands):
|  | Shares |  | Weighted Average Exercise Price |  | Options Exercisable at End of Period |  | Weighted Average Exercise Price of Exercisable Options |  | Weighted Average Fair Value of Options Granted During the Period |  | Aggregate Intrinsic Value
Outstanding at December 31, 2020 |  | 4,964 |  |  | $ | 146.69 |  |  | 3,994 |  |  | $ | 130.37 |  |  |  |  | $ | 626,107 |
Granted |  | 1,081 |  |  | 261.27 |  |  |  |  |  |  | $ | 66.87 |  |  |
Exercised |  | (585) |  |  | 81.05 |  |  |  |  |  |  |  |  | 109,727 |
Forfeited |  | (20) |  |  | 231.52 |  |  |  |  |  |  |  |  |
Outstanding at September 30, 2021 |  | 5,440 |  |  | $ | 176.24 |  |  | 3,765 |  |  | $ | 144.74 |  |  |  |  | $ | 463,948 |
Expected to vest as of September 30, 2021 |  | 1,675 |  |  | $ | 247.05 |  |  |  |  |  |  |  |  |
Schedule of Weighted-Average Assumptions | The fair value of stock option awards granted was estimated using the Black-Scholes option pricing model, as well as the Monte-Carlo simulation model for market-based options, with the following weighted-average assumptions for grants or modifications during the nine months ended September 30, 2021 and 2020:
|  | September 30,
|  | 2021 |  | 2020
Risk-free interest rate |  | 0.55 | % |  | 0.38 | %
Dividend yield |  | — |  |  | — |
Expected volatility |  | 35.75 | % |  | 30.91 | %
Expected life (in years) |  | 3.4 |  | 3.9
Summary of Changes in Number of Shares of Restricted Stock and Restricted Stock Units | The following table summarizes the changes in the number of shares of restricted stock and restricted stock units for the nine months ended September 30, 2021 (shares in thousands):
|  | Shares |  | Weighted Average Grant Date Fair Value
Outstanding at December 31, 2020 |  | 174 |  |  | $ | 265.29 |
Granted |  | 213 |  |  | 272.83 |
Vested |  | (72) |  |  | 258.16 |
Canceled or forfeited |  | (29) |  |  | 283.14 |
Outstanding at September 30, 2021 |  | 286 |  |  | $ | 278.40 |

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- Definition Tabular disclosure for stock option plans. Includes, but is not limited to, outstanding awards at beginning and end of year, grants, exercises, forfeitures, and weighted-average grant date fair value. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Disclosure of the number and weighted-average grant date fair value for restricted stock and restricted stock units that were outstanding at the beginning and end of the year, and the number of restricted stock and restricted stock units that were granted, vested, or forfeited during the year. + References No definition available. + Details
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- Definition Tabular disclosure of cost not yet recognized and weighted-average period over which cost is expected to be recognized for nonvested award under share-based payment arrangement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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