Stock-Based Compensation - Status of Our Stock Options (Detail) - $ / shares	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of Shares
Number of shares, outstanding	5,318,759	6,839,417	6,342,526
Number of shares, granted	845,120	969,720	2,457,102
Number of shares, exercised	(2,310,934)	(2,309,451)	(1,570,211)
Number of shares, forfeited	(67,004)	(180,927)	(390,000)
Number of shares, outstanding	3,785,941	5,318,759	6,839,417
Number of shares, exercisable	1,622,132
Weighted Average Exercise Price
Weighted average exercise price, outstanding (in dollars per share)	$ 9.97	$ 7.63	$ 6.51
Weighted average exercise price, granted (in dollars per share)	28.33	19.70	9.03
Weighted average exercise price, exercised (in dollars per share)	7.96	6.83	5.48
Weighted average exercise price, forfeited (in dollars per share)	16.37	13.34	7.15
Weighted average exercise price, outstanding (in dollars per share)	15.21	$ 9.97	$ 7.63
Weighted average exercise price, exercisable (in dollars per share)	$ 9.53

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Gross number of share options (or share units) granted during the period.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Number of share options (or share units) exercised during the current period.

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