Basic income (loss) per common share is computed as net income (loss) divided by the basic weighted average common shares outstanding of 35.6 million shares for the three and six months ended June 30, 2019 and 35.5 million and 35.4 million shares for the three and six months ended June 30, 2018, respectively. The calculation of diluted income (loss) per common share includes the effect of any dilutive equity incentive instruments. The Company uses the treasury stock method to calculate the effect of outstanding dilutive equity incentive instruments, which requires the Company to compute total proceeds as the sum of the amount the employee must pay upon exercise of the award and the amount of unearned stock-based compensation costs attributable to future services.

Equity incentive instruments for which the total employee proceeds from exercise exceed the average fair value of the same equity incentive instrument over the period have an anti-dilutive effect on income per common share during periods with net income, and accordingly, the Company excludes them from the calculation. Anti-dilutive equity instruments of approximately 1,515,430 and 188,885 common shares were excluded from the computation of diluted net income per common share for the three months ended June 30, 2019 and 2018, respectively. Anti-dilutive equity instruments of approximately 1,556,298 were excluded from the computation of diluted net income per common share for the six months ended June 30, 2019. Due to the net loss incurred during the six months ended June 30, 2018, the assumed exercise of all equity incentive instruments was anti-dilutive and, therefore, not included in the diluted loss per common share calculation for those periods.

The following is a reconciliation of the average shares outstanding used to compute basic and diluted income (loss) per common share:

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Basic weighted average common shares outstanding		35,595,718		35,530,356		35,619,145		35,449,298
Effect of dilutive securities		130,190		533,752		179,944		—
Diluted weighted average common shares outstanding		35,725,908		36,064,108		35,799,089		35,449,298

No cash dividends were paid during the three and six months ended June 30, 2019 and 2018.