17.  Net Loss Per Common Share

Basic loss per share of common stock is computed using the weighted average number of common shares outstanding for the period. Diluted loss per share is computed without consideration to potentially dilutive instruments because the Company incurred losses in the three months ended June 30, 2019 which would make these instruments anti-dilutive. As of June 30, 2019 and 2018, the number of anti-dilutive stock options and restricted stock units excluded from diluted net loss per common share computations was approximately 3.2 million and 2.5 million, respectively. As of June 30, 2019 and 2018, the number of PRSUs subject to performance conditions which have not been satisfied have been excluded from diluted net loss per common share computations was approximately 0.3 million. As of June 30, 2019 and 2018, the number of warrants excluded from diluted net loss per common share computations was approximately 6.8 million and 2.7 million, respectively.