Income Per Share - Additional Information (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares excluded from diluted weighted average shares outstanding (in shares)	0.5	0.6	0.4
Anti-dilutive shares excluded form diluted weighted average shares outstanding due to performance conditions not met (in shares)	0.2	0.1	0.0
Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares excluded from diluted weighted average shares outstanding (in shares)	6.9	3.0