(Number of shares in millions)	2020		2019		2018
Common stock:
Balance, beginning of year	109.3		108.5		107.8
Activity under stock plans		0.4		0.8		0.7
Balance, end of year	109.7		109.3		108.5
Treasury stock:
Balance, beginning of year	25.7		23.7		18.2
Repurchased		0.4		2.0		5.5
Balance, end of year	26.1		25.7		23.7
Common stock outstanding	83.6		83.6		84.8

In May 2018, our Board authorized the repurchase of $500 million of the Company’s stock (“2018 Repurchase Plan”). During 2020, 2019 and 2018, the Company spent $24.6 million, $143.0 million and $357.7 million to repurchase common stock, respectively. At December 31, 2020, we have $217.2 million remaining under the 2018 Repurchase Plan.

Dividends per share of common stock for 2020, 2019, and 2018, were $0.17, $0.64 , and $0.55 , respectively. For the years ended December 31, 2020 and 2019, we paid $14.2 million and $54.2 million in dividends, respectively. In response to the COVID-19 pandemic, we suspended our dividend payments and stock repurchases in April 2020.

On April 6, 2020, the Company declared a dividend of one preferred share purchase right (a “right”) for each outstanding share of the Company’s common stock and adopted a stockholder rights plan, as set forth in the rights agreement entered into as of April 6, 2020, between the Company and American Stock Transfer & Trust Company, LLC, as rights agent. The dividend was payable on April 16, 2020 to stockholders of record of the Company’s common stock on such date. In general, the rights plan works by imposing a significant penalty upon any person or group which acquires 15% or more of the outstanding common stock without the prior approval of the board. If the rights become exercisable, each right will allow its holder to purchase from the Company one one-hundredth of a share of Series A Junior Participating Preferred Stock for $150.00. This portion of a preferred share will give the stockholder approximately the same dividend, voting and liquidation rights as would one share of common stock. The rights will not be exercisable until ten days after the public announcement that a person or group has become an “acquiring person” (as defined in the rights agreement) by obtaining beneficial ownership of 15% or more of our outstanding common stock. Prior to exercise, the right does not give its holder any dividend, voting, or liquidation rights. The rights will expire on April 6, 2021. The rights were not exercisable at any time through December 31, 2020.