13. 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):


	Year Ended December 31,
	2018		2017		2016
Net income attributable to common shares	$	77,922	$	62,605	$	50,371
Weighted-average common shares outstanding - basic		34,957,244		33,792,759		32,289,414
Effect of potentially dilutive common shares:
Stock options		47,338		88,399		192,464
Unvested awards		132,913		177,791		250,181
Weighted-average common shares outstanding - diluted		35,137,495		34,058,949		32,732,059
Net income per share attributable to common shares
Basic	$	2.23	$	1.85	$	1.56
Diluted	$	2.22	$	1.84	$	1.54

In the calculations above, we have excluded weighted-average potentially dilutive securities of 132,749, 24,961, and 29,618 for the years ended December 31, 2018, 2017, and 2016, respectively, as their effect would have been antidilutive.