13. Earnings Per Share Attributable to Common Stockholders

Basic earnings per share is computed by dividing net income attributable to common stockholders by the weighted-average number of common shares outstanding during the period without consideration for common stock equivalents. Diluted net income per share attributable to common stockholders is computed by dividing net income by the weighted-average number of common shares outstanding during the period and potentially dilutive common stock equivalents, including stock options, restricted stock units and restricted stock awards, except in cases where the effect of the common stock equivalent would be antidilutive. Potential common stock equivalents consist of common stock issuable upon exercise of stock options and vesting of restricted stock units and restricted stock awards using the treasury stock method. The calculation of weighted-average dilutive shares outstanding for the year ended December 31, 2017 was impacted by the adoption of ASU 2016-09. See Note 2, Summary of Significant Accounting Policies, for additional details.

The following table presents the calculation of basic and diluted net income per share attributable to common stockholders for the years ended December 31, 2017, 2016 and 2015:

		Year Ended December 31, 2017
		Income (Numerator)		Shares (Denominator)		Per Share Amount
	(in thousands, except per share data)
Basic EPS
Net income attributable to common stockholders		$	98,983		86,297	$	1.15
Effect of Dilutive Securities
Stock options			—		1,059
Restricted stock units			—		826
Diluted EPS
Net income attributable to common stockholders		$	98,983		88,182	$	1.12

		Year Ended December 31, 2016
		Income (Numerator)		Shares (Denominator)		Per Share Amount
	(in thousands, except per share data)
Basic EPS
Net income attributable to common stockholders		$	49,557		85,069	$	0.58
Effect of Dilutive Securities
Stock options			—		792
Restricted stock units and restricted stock awards			—		274
Diluted EPS
Net income attributable to common stockholders		$	49,557		86,135	$	0.58

		Year Ended December 31, 2015
		Income (Numerator)		Shares (Denominator)		Per Share Amount
	(in thousands, except per share data)
Basic EPS
Net income attributable to common stockholders		$	38,077		84,076	$	0.45
Effect of Dilutive Securities
Stock options			—		1,594
Restricted stock units and restricted stock awards			—		36
Diluted EPS
Net income attributable to common stockholders		$	38,077		85,706	$	0.44

During the year ended December 31, 2016, the Company repurchased and retired 724,473 shares of its common stock at a weighted-average share price of $20.37, or an aggregate of $14.8 million. The repurchases resulted in a reduction of the outstanding shares used to calculate the weighted-average common shares outstanding for basic and diluted net earnings per share from the dates of the repurchases. See Note 11, Stockholders’ Equity, for additional details.

The number of shares of common stock underlying stock-based awards excluded from the calculation of diluted net income per share attributable to common stockholders because their effect would have been antidilutive for the years ended December 31, 2017, 2016 and 2015 were as follows:

	Year Ended December 31,
	2017		2016		2015
Anti-dilutive shares underlying stock-based awards:
Stock options		—		552,108		2,380,813
Restricted stock units		35,646		212,170		464,930