Net Income Per Share and Stockholders' Equity Net Income Per Share and Stockholders' Equity, Share Repurchases (Details) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Equity [Abstract]
Weighted-average repurchase price (dollars per share)		$ 96.18	$ 100.28	$ 82.97
Total cost of repurchased common shares	[1]	$ 42.9	$ 61.9	$ 77.8

[1] Weighted-average repurchase price (dollars per share) for the years ended December 31, 2019, December 31, 2018 and December 31, 2017 was $96.18, $100.28 and $82.97, respectively. At December 31, 2019, $105.6 million remained available to repurchase our common shares pursuant to the stock repurchase program.