12. Earnings per Share

Basic earnings per common share is determined by dividing earnings attributable to common stockholders by the weighted-average number of common shares outstanding during the period, without consideration of common stock equivalents. Diluted earnings per share is computed by dividing the earnings attributable to common stockholders by the weighted-average number of common share equivalents outstanding for the period. The treasury stock method is used to determine the dilutive effect of the Company’s stock option grants, SAR, warrants, ESPP awards and the 2023 Notes.

The following common stock equivalents were excluded in the calculation of diluted earnings per share because their inclusion would be anti-dilutive as applied to the earnings from continuing operations applicable to common stockholders for the three and nine months ended September 30, 2018 and 2017:


	Three Months ended September 30,		Nine Months ended September 30,
	2018	2017	2018	2017
	(unaudited)		(unaudited)
Warrants to purchase common stock	4,293,022	—	3,382,253	—
Convertible notes	79,444	—	70,204	—
Convertible notes hedges	80	—	70	—
Stock options, SAR and ESPP awards	165,675	15,170	180,100	105,699

The following table sets forth the computation of basic and diluted net earnings per share for the three and nine months ended September 30, 2018 and 2017, in thousands of dollars, except share and per share amounts:


	Three Months ended September 30,				Nine Months ended September 30,
	2018		2017		2018		2017
	(unaudited)				(unaudited)
Numerator, in thousands:
Net earnings used for calculation of basic EPS	$	28,011	$	15,961	$	85,100	$	43,626

Interest expense on convertible debt		—		(14)		—		134
Changes in fair value of derivative liabilities		—		—		—		(76)
Loss on extinguishment of debt		—		91		—		295
Loss on extinguishment of outstanding debt, as if converted		—		(273)		—		(321)
Total adjustments		—		(196)		—		32
Net earnings used for calculation of diluted EPS	$	28,011	$	15,765	$	85,100	$	43,658

Denominator:
Weighted average shares outstanding, basic		52,227,630		51,046,375		51,897,240		50,583,726

Effect of dilutive potential common shares:
Shares underlying Convertible Senior Notes		—		56,484		—		382,230
Shares issuable to settle interest make-whole derivatives		—		—		—		7,013
Stock options and SAR		2,012,217		2,525,530		2,201,090		2,254,464
Total dilutive potential common shares		2,012,217		2,582,014		2,201,090		2,643,707
Weighted average shares outstanding, diluted		54,239,847		53,628,389		54,098,330		53,227,433

Net earings per share, basic	$	0.54	$	0.31	$	1.64	$	0.86
Net earnings per share, diluted	$	0.52	$	0.29	$	1.57	$	0.82