Earnings Per Common Share

Basic and diluted earnings per common share are computed by dividing net income by the weighted-average number of basic and diluted common shares outstanding, respectively. The weighted-average number of diluted common shares includes the impact of dilutive securities, including outstanding stock options and unvested restricted stock and restricted stock units. The table below reconciles the weighted-average basic and diluted common shares outstanding for 2017, 2016 and 2015:



	Year Ended December 31, 2017
	2017	2016	2015
	(in thousands)
Weighted average number of common shares outstanding - basic	73,355	72,754	71,826
Effect of dilutive securities⁽¹⁾	993	720	686
Weighted average number of common shares outstanding - diluted	74,348	73,474	72,512

⁽¹⁾ Certain outstanding stock option awards are anti-dilutive and were therefore excluded from the calculation of the weighted average number of diluted common shares outstanding. For the year ended December 31, 2017, options to purchase less than a thousand shares, having a weighted average exercise price of $39.38, were excluded from the computation. For the years ended December 2016 and 2015, the computation excluded options to purchase 0.5 million and 0.9 million shares, having weighted average exercise prices of $34.14 and $29.34, respectively.