Basic net income per common share is based on the weighted average number of common shares outstanding and the minimum number of shares to be issued upon settlement of the stock purchase contracts issued under the tangible equity units. Diluted net income per common share is based on the weighted average number of common shares outstanding, potentially dilutive shares, and the expected number of shares to be issued upon settlement of the stock purchase contracts issued under the tangible equity units, based on the applicable market value of our common stock. The dilutive effect of employee stock-based compensation is included in the computation of diluted net income per common share. The dilutive effect of stock-based compensation is calculated using the treasury stock method and expected proceeds upon exercise or issuance of the stock-based compensation. The treasury stock method assumes that the proceeds from stock-based compensation are used to purchase the Company’s common stock at the average market price during the period. The following table summarizes the shares, in thousands, used in computing basic and diluted net income per common share:



	Three Months Ended
	March 31,
	2020	2019
Average common shares outstanding during the period for basic computation	236,122	178,213
Effect of dilutive securities:
Issuance of common stock from private placement	17,853	-
Tangible equity units	607	-
Employee stock-based compensation	472	339
Average common shares outstanding during the period for diluted computation	255,054	178,552

For the three months ended March 31, 2020, the average common shares outstanding during the period for diluted computation reflects the impact of the issuance of common stock from the March 16, 2020 private placement as if the shares were issued on January 1, 2020.

For the three months ended March 31, 2020, the average common shares outstanding during the period for basic computation includes the weighted-average impact of 10,215,189 shares, based on the minimum number of shares of 9,091,432 to be issued in April 2022 upon settlement of the stock purchase contracts issued in April 2019 under the tangible equity units. Further, for the three months ended March 31, 2020, average common shares outstanding during the period for diluted computation includes the impact of the additional shares to be issued in April 2022 upon settlement of the stock purchase contracts based on the threshold appreciation price of $42.41.

For the three months ended March 31, 2020, all of the Company’s employee stock options were included in the calculations of diluted net income per share as the calculated cost to exercise employee stock options was less than the average market price of the Company’s common stock during this period. For the three months ended March 31, 2019, employee stock options to purchase 776,211 shares of common stock were excluded from the calculation of diluted net income per share as the calculated cost to exercise the stock options was greater than the average market price of the Company’s common stock

during this period. Additionally, the dilutive effect of performance share units and restricted share units granted are included in the Company’s calculation of diluted net income per share.