Stock Option Summary (Details) - Share-based Payment Arrangement, Option [Member] - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
[Line Items]
Outstanding, beginning balance (in shares)	433	458	458
Outstanding, beginning balance, weighted average exercise price per share (in dollars per share)	$ 61.95	$ 56.38	$ 56.38
Outstanding, weighted average remaining contractual life	6 years 1 month 6 days	7 years	6 years 10 months 24 days	7 years
Outstanding, beginning balance, aggregate intrinsic value	$ 14,697	$ 12,641	$ 12,641
Granted (in shares)	0	80
Granted, weighted average exercise price (in dollars per share)		$ 84.38
Granted, weighted average grant date fair value	$ 0	$ 26.21
Exercised (in shares)	(34)	(49)
Exercised, weighted average exercise price (in dollars per share)	$ 67.21	$ 50.90
Exercised, aggregate intrinsic value	$ 1,215	$ 1,189
Forfeited (in share)	(6)	(5)
Forfeited, weighted average grant date fair value (in dollars per share)	$ 83.33	$ 83.80
Outstanding, ending balance (in shares)	393	484	433	458
Outstanding, ending balance, weighted average exercise price per share (in dollars per share)	$ 61.18	$ 61.30	$ 61.95	$ 56.38
Outstanding, weighted average remaining contractual life	6 years 1 month 6 days	7 years	6 years 10 months 24 days	7 years
Outstanding, ending balance, aggregate intrinsic value	$ 6,496	$ 3,816	$ 14,697	$ 12,641
Exercisable (in shares)	317
Exercisable, weighted average exercise price (in dollars per share)	$ 56.51
Exercisable, weighted average remaining contractual term	5 years 7 months 6 days
Exercisable, aggregate intrinsic value	$ 6,361