8. Earnings (loss) Per Share

Basic earnings (loss) per share is computed on the basis of weighted average outstanding common shares. Diluted earnings (loss) per share is computed on the basis of basic weighted average outstanding common shares adjusted for the dilutive effect of stock options and other outstanding dilutive securities.

The following table reconciles the average share amounts used to compute both basic and diluted earnings (loss) per share (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Weighted average shares outstanding:
Basic weighted average shares outstanding		115,889		118,254		115,615		117,096
Add: Dilutive effect of stock options		1,603		1,489		—		—

Diluted weighted average shares outstanding		117,492		119,743		115,615		117,096

The diluted earnings per share computation excludes 1.2 million and 3.3 million options to purchase shares, contingently issuable shares, and restricted share awards during the three months ended September 30, 2018 and 2017, respectively, as their effect would be anti-dilutive. The diluted loss per share computation excludes 8.0 million and 10.1 million options to purchase shares, contingently issuable shares, and restricted share awards during the nine months ended September 30, 2018 and 2017, respectively, as their effect would be anti-dilutive.

Common stock outstanding as of September 30, 2018 and December 31, 2017, was 115,981,696 and 117,096,731, respectively.