Diluted earnings attributable to shareholders per share is computed using the weighted average number of common shares and dilutive potential common shares outstanding. Dilutive potential shares represent outstanding stock options, including purchase options under the Company's employee stock purchase plan and unvested RSU. Basic earnings attributable to shareholders per share is calculated using the weighted average number of common shares outstanding without taking into consideration dilutive potential common shares outstanding.

The following table reconciles the numerator and the denominator of the basic and diluted per share computations for earnings attributable to shareholders.



	Net earnings attributable to shareholders		Weighted average shares	Earnings per share
2018
Basic earnings attributable to shareholders	$	618,199	174,133	$	3.55
Effect of dilutive potential common shares	—		3,700	—
Diluted earnings attributable to shareholders	$	618,199	177,833	$	3.48
2017
Basic earnings attributable to shareholders	$	489,345	179,247	$	2.73
Effect of dilutive potential common shares	—		2,419	—
Diluted earnings attributable to shareholders	$	489,345	181,666	$	2.69
2016
Basic earnings attributable to shareholders	$	430,807	181,282	$	2.38
Effect of dilutive potential common shares	—		1,422	—
Diluted earnings attributable to shareholders	$	430,807	182,704	$	2.36

Substantially all outstanding potential common shares shares in 2018 and 2017 were dilutive. In 2016, 9.2 million of potential common shares were excluded from the computation of diluted earnings per share because the effect would have been antidilutive.