12. Earnings Per Share

Basic net income per share is calculated by dividing the net income attributable to common shares by the weighted-average number of common shares outstanding during the period. Diluted net income per share adjusts basic net income per share for the effects of potentially dilutive common shares, if the effect is not antidilutive. Potentially dilutive common stock consists of shares issuable under the 2010 Plan. The following is a summary of basic and diluted net income per share (in thousands, except share and per share amounts):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Net income attributable to common shares	$	18,600	$	15,758	$	58,291	$	47,693
Weighted-average common shares outstanding - basic		35,512,091		33,878,881		34,504,790		33,758,971
Effect of potentially dilutive common shares:
Stock options		45,453		59,201		49,349		98,660
Unvested awards		163,934		176,087		139,696		176,211
Weighted-average common shares outstanding - diluted		35,721,478		34,114,169		34,693,835		34,033,842
Net income per share attributable to common shares
Basic	$	0.52	$	0.47	$	1.69	$	1.41
Diluted	$	0.52	$	0.46	$	1.68	$	1.40

In the calculations above, we have excluded weighted-average potentially dilutive securities of 1,003 and 1,205 for the three months ended September 30, 2018, and 2017, respectively, and 121,373 and 109,953 for the nine months ended September 30, 2018, and 2017, respectively, as their effect would have been antidilutive.