Net Income Per Share (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Mar. 04, 2016
Stock Repurchase Program, Authorized Amount					$ 500,000
Treasury Stock, Shares, Acquired	1,138,196		1,949,581
Treasury Stock Acquired, Average Cost Per Share	$ 54.27		$ 56.42
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 390,003		$ 390,003
Performance Shares [Member]
Antidilutive securities excluded from EPS	137,000	125,000	137,000	125,000