Share Repurchase Programs (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2015
December 2015 Program
Accelerated Share Repurchases [Line Items]
Common stock repurchases	$ 65.9	$ 25.7
Common Stock | December 2015 Program
Accelerated Share Repurchases [Line Items]
Repurchased and retired shares (in shares)	933,000	380,000
December 2015 Program
Accelerated Share Repurchases [Line Items]
Maximum number of share repurchases authorization (no more than 1.5 million) (in shares)			1,500,000.0
Number of shares authorized to be repurchased (in shares)			2,000,000
December 2015 Program | December Two Thousand Thirteen Anti Dilutive Share Repurchase Program
Accelerated Share Repurchases [Line Items]
Number of shares authorized to be repurchased (in shares)			500,000.0