Stockholders' Equity (Details) - USD ($)	3 Months Ended						9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Jun. 30, 2018	Jun. 30, 2017	Aug. 01, 2018	Aug. 01, 2017
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Amount of stock repurchase authorization										$ 200,000,000
Treasury Stock, Shares, Acquired							1,608,537
Payments for Repurchase of Common Stock							$ 74,900,000	$ 60,600,000
Amount remaining under stock repurchase authorization		$ 125,100,000					$ 125,100,000
Dividends, Common Stock [Abstract]
Cash dividends declared per common share (in dollars per share)		$ 0.125	$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.375	$ 0.30
Cash dividends paid per common share (in dollars per share)		$ 0.125	$ 0.10	$ 0.10	$ 0.10	$ 0.10
Subsequent Event [Member]
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Amount of stock repurchase authorization									$ 400,000,000
Dividends, Common Stock [Abstract]
Cash dividends declared per common share (in dollars per share)	$ 0.125