Weighted Average Shares

12 Months Ended

Dec. 31, 2018

Weighted-average shares were calculated as follows (in thousands):



	Year Ended December 31,
	2018	2017	2016
Basic weighted-average common shares outstanding	172,333	173,287	170,676
Effect of dilutive stock options	5,073	6,264	3,468
Diluted weighted-average common and common-equivalent shares outstanding	177,406	179,551	174,144

Stock options to purchase 2,650,164, 3,363,141, and 4,391,598 shares of common stock, on a weighted-average basis, were outstanding in 2018, 2017, and 2016, respectively, but were not included in the calculation of dilutive net income per share because they were anti-dilutive.