Stock Options and Employee Stock Purchase Plan - Stock Option Activity (Details) - USD ($)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of Shares
Beginning balance (in shares)	518,341	707,777	375,675
Granted (in shares)	0	0	400,000
Exercised (in shares)	(42,740)	(189,436)	(67,898)
Canceled (in shares)	0	0	0
Ending balance (in shares)	475,601	518,341	707,777
Exercisable (in shares)	175,601	163,741	298,577
Vested and expected to vest (in shares)	393,281
Weighted-Average Exercise Price
Beginning balance (in usd per share)	$ 65.77	$ 56.84	$ 31.30
Granted (in usd per share)	0	0	75.03
Exercised (in usd per share)	23.11	32.39	22.68
Canceled (in usd per share)	0	0	0
Ending balance (in usd per share)	69.61	65.77	56.84
Exercisable (in usd per share)	60.35	$ 45.94	$ 32.15
Vested and expected to vest (in usd per share)	$ 68.47
Weighted-Average Remaining Contractual Life (In Years)
Options outstanding at December 31, 2020	6 years 2 months 12 days
Exercisable at December 31, 2020	4 years 8 months 12 days
Vested and expected to vest at December 31, 2020	6 years
Aggregate Intrinsic Value
Options outstanding at December 31, 2020	$ 13,355,721
Exercisable at December 31, 2020	6,557,721
Vested and expected to vest at December 31, 2020	$ 11,490,350

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

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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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