Stock-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2021	Dec. 31, 2020
Options
Beginning balance (in shares)	552,669
Granted (in shares)	126,794
Exercised (in shares)	(74,343)
Canceled (in shares)	(26,037)
Ending balance (in shares)	579,083	552,669
Exercisable at period end (in shares)	336,940
Weighted Average Exercise Price
Beginning balance (in dollars per share)	$ 69.82
Granted (in dollars per share)	81.21
Exercised (in dollars per share)	52.13
Canceled (in dollars per share)	74.73
Ending balance (in dollars per share)	73.11	$ 69.82
Exercisable (in dollars per share)	$ 58.96
Weighted Average Remaining Contractual Life
Outstanding, weighted average remaining contractual life (in years)	6 years 3 months 18 days	6 years 1 month 6 days
Exercisable weighted average remaining contractual life (in years)	5 years 8 months 12 days
Aggregate Intrinsic value (in millions)
Outstanding, aggregate intrinsic value	$ 9.0	$ 4.2
Exercisable, aggregate intrinsic value	$ 9.4

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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- Definition

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.