Stock Repurchases (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Feb. 13, 2017
Equity, Class of Treasury Stock [Line Items]
Increase in number of shares authorized for repurchase					1,000,000,000,000
Number of shares authorized for repurchase		769,713
Common stock repurchased, shares		712,448	342,928	610,260
Common stock repurchased, value		$ 300.4	$ 129.1	$ 123.5
Open Market [Member]
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased, shares	[1]	669,752	336,743	588,580
Common stock repurchased, value	[1]	$ 282.2	$ 127.1	$ 119.1
Other [Member]
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased, shares	[2]	42,696	6,185	21,680
Common stock repurchased, value	[2]	$ 18.2	$ 2.0	$ 4.4

[1] Represents repurchases under authorizations by the board of directors for the repurchase of shares by us from time to time in the open market or in privately negotiated transactions. On November 7, 2019, the board of directors authorized the repurchase of up to one million shares of our common stock in addition to the board’s prior authorizations. As of December 31, 2019, we had authorization to repurchase 769,713 shares of our common stock.

[2] Represents shares of common stock released to us by team members as payment of tax withholdings upon the vesting of restricted stock and restricted stock units and the conversion of restricted stock units to common stock.