Summary of Significant Accounting Policies (Net Income Per Share) (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted Average Number of Shares Outstanding, Basic	58,066	64,905	71,746
Weighted Average Number of Shares Outstanding, Diluted	58,947	65,625	72,410
Employee Stock Option [Member]
Incremental Weighted Average Shares Attributable to Dilutive Effect [Abstract]
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	15	1	13
Restricted Stock Units (RSUs) [Member]
Incremental Weighted Average Shares Attributable to Dilutive Effect [Abstract]
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	866	719	651