Net Income per Share - Additional Information (Details) - USD ($) shares in Millions, $ in Millions	Aug. 15, 2018	Feb. 20, 2018	Sep. 30, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Increase in authorized amount to be repurchased	$ 75.0	$ 25.0
Stock Repurchase Program, Authorized Amount			$ 235.0	$ 135.0
Cumulative amount repurchased			$ 186.8
Cumulative number of shares repurchased			14.2