Earnings Per Share

The following table sets forth the computation of basic and diluted net income per common share for the years indicated (in thousands, except per share data):



	Year Ended December 31,
	2018			2017			2016
Net income	$	166,111		$	67,821		$	100,656
Dividends and undistributed earnings allocated to unvested shares	(1,184		)	(571		)	—
Preferred dividends	—			—			(21		)
Net income available to common stockholders	$	164,927		$	67,250		$	100,635
Income per common share:
Basic	$	2.07		$	0.92		$	1.40
Diluted	2.07			0.92			1.40
Weighted average common shares:
Basic	79,662			73,247			71,910
Effect of dilutive securities:
Stock options	7			12			5
Restricted stock units	2			—			—
Diluted	79,671			73,259			71,915

At December 31, 2018, 32,316 potentially dilutive shares of common stock issuable upon exercise of stock options were excluded from the computation of diluted earnings per share because of their antidilutive effect.

At December 31, 2017, United had the following potentially dilutive instruments outstanding: a warrant to purchase 219,909 shares of common stock at $61.40 per share; 60,287 shares of common stock issuable upon exercise of stock options; and 663,817 shares of common stock issuable upon completion of vesting of restricted stock awards.

At December 31, 2016, United had the following potentially dilutive instruments outstanding: a warrant to purchase 219,909 shares of common stock at $61.40 per share; 72,665 shares of common stock issuable upon exercise of stock options; and 690,970 shares of common stock issuable upon completion of vesting of restricted stock awards.