Shareholders' Equity - Share Repurchase and Dividends (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	May 31, 2019
Shareholders' Equity
Aggregate cost of common stock repurchased during the period		$ 0.1	$ 0.2
Dividend declared per common share (in dollars per share)	$ 0.16
May 2019 Repurchase Program
Shareholders' Equity
Amount approved for repurchase of common stock				$ 300.0
Common stock repurchased during the period (in shares)	2,711,952	3,323,104
Aggregate cost of common stock repurchased during the period	$ 123.2	$ 142.3
Remaining authorization amount for repurchase of common stock	$ 34.5