Shareholders' Equity - Stock Option Activity (Details) $ / shares in Units, $ in Millions		9 Months Ended
	Sep. 30, 2021 USD ($) $ / shares shares	Sep. 30, 2021 USD ($) $ / shares shares	Sep. 30, 2020 USD ($)
Stock options, Shares Subject to Options
Outstanding at the beginning of the period (in shares) | shares		1,856,176
Granted (in shares) | shares		79,632
Exercised (in shares) | shares		(515,692)
Outstanding at the end of the period (in shares) | shares	1,420,116	1,420,116
Exercisable at the end of the period (in shares) | shares	1,158,452	1,158,452
Exercisable and expected to vest at the end of the period (in shares) | shares	1,384,099	1,384,099
Stock options, Weighted Average Option Price
Outstanding at the beginning of the period (in dollars per share) | $ / shares		$ 25.32
Granted (in dollars per share) | $ / shares		85.10
Exercised (in dollars per share) | $ / shares		20.40
Outstanding at the end of the period (in dollars per share) | $ / shares	$ 30.45	30.45
Exercisable at the end of the period (in dollars per share) | $ / shares	24.66	24.66
Exercisable and expected to vest at the end of the period (in dollars per share) | $ / shares	$ 29.68	$ 29.68
Stock options, additional information
Weighted Average Remaining Contractual Term, Outstanding		4 months 9 days
Weighted Average Remaining Contractual Term, Exercisable	3 months 24 days
Weighted Average Remaining Contractual Term, Exercisable and expected to vest	4 months 6 days
Aggregate Intrinsic Value, Outstanding | $	$ 68.2	$ 68.2
Aggregate Intrinsic Value, Exercisable | $	61.9	61.9
Aggregate Intrinsic Value, Exercisable and expected to vest | $	$ 67.5	67.5
Intrinsic value of options exercised | $		$ 31.8	$ 2.2