Shareholders' Equity - Stock Option Activity (Details) - Stock options - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock options, Shares Subject to Options
Outstanding at the beginning of the period (in shares)	1,988,696
Granted (in shares)	125,794
Exercised (in shares)	(241,915)
Forfeited /Expired (in shares)	(16,399)
Outstanding at the end of the period (in shares)	1,856,176	1,988,696
Exercisable at the end of the period (in shares)	1,546,061
Exercisable and expected to vest at the end of the period (in shares)	1,818,104
Stock options, Weighted Average Option Price
Outstanding at the beginning of the period (in dollars per share)	$ 23.43
Granted (in dollars per share)	45.54
Exercised (in dollars per share)	20.29
Forfeited (in dollars per share)	20.98
Outstanding at the end of the period (in dollars per share)	25.32	$ 23.43
Exercisable at the end of the period (in dollars per share)	22.14
Exercisable and expected to vest at the end of the period (in dollars per share)	$ 24.95
Stock options, additional information
Weighted Average Remaining Contractual Term, Outstanding	4 years 2 months 12 days	4 years 10 months 24 days
Weighted Average Remaining Contractual Term, Exercisable	3 years 10 months 24 days
Weighted Average Remaining Contractual Term, Exercisable and expected to vest	4 years 2 months 12 days
Aggregate Intrinsic Value, Outstanding	$ 53.5	$ 54.8
Aggregate Intrinsic Value, Exercisable	49.5
Aggregate Intrinsic Value, Exercisable and expected to vest	53.1
Intrinsic value of options exercised	$ 6.1	$ 15.2	$ 8.0