9. Equity

Common Stock and Share Repurchase Plan

On October 20, 2015, our Board of Directors increased the number of shares authorized to be repurchased under our share repurchase plan by 7.5 million shares and extended the duration of the plan through December 31, 2018. We repurchase shares through open market purchases under plans complying with Rule 10b5-1 under the Securities Exchange Act of 1934, as amended (the “Exchange Act”). During the six months ended June 30, 2018, we repurchased 592,564 shares of our common stock at an average cost of $84.38 per share for a total of $50.0 million. Since initiating the share repurchase plan in 1994, we have repurchased approximately 23.1 million shares at an average cost of $32.94 per share. As of June 30, 2018, we had authorization under the plan to purchase approximately 7.5 million shares, or about 10% of our current outstanding shares. Repurchased and subsequently retired shares are restored to the status of authorized but unissued shares.

Common stock and additional paid-in capital activity included the following:


	Three Months Ended				Six Months Ended
	June 30, 2018				June 30, 2018
				Weighted Average				Weighted Average
	Shares	Amount		Exercise Price	Shares	Amount		Exercise Price
	(in millions, except share and per share amounts)
Stock-based compensation(1)	15,574	$	12.9		285,007	$	13.9
Stock options exercised	—		—		48,275		2.8	$	57.91
Share repurchases	—		—		(592,564)		(50.0)
Total	15,574	$	12.9		(259,282)	$	(33.3)

⁽¹⁾

The six months ended June 30, 2018 amount is comprised of stock-based compensation expense of $19.3 million reduced by $5.4 million of payments we made to tax authorities on our employees’ behalf for shares withheld related to net share settlements.

Dividends

On July 25, 2018, our Board of Directors declared the 2018 third quarter cash dividend of $0.50 per share. The dividend is payable on September 7, 2018 to stockholders of record as of August 17, 2018.

During the second quarters of 2018 and 2017, we declared and paid quarterly dividends of $0.50 and $0.45 per share, or $36.1 million and $32.8 million in total, respectively. During the six months ended June 30, 2018 and 2017, we declared and paid quarterly dividends of $1.00 and $0.90 per share, or $72.6 million and $65.6 million in total, respectively. During the six months ended June 30, 2018 and 2017, we paid $2.0 million and $0.9 million in dividend equivalents with respect to vested restricted stock units (“RSUs”), respectively.

Stock-Based Compensation

We make annual grants of long-term incentive awards to officers and key employees in the forms of service-based and performance-based RSUs that generally have approximately 3-year vesting periods. The performance-based RSU awards are subject to both service and performance goal criteria. We also make annual grants of stock to the non-employee members of the Board of Directors that include dividend rights and vest immediately upon grant. The fair value of the RSUs and stock grants is determined based on the closing stock price of our common stock on the grant date.

A summary of the status of our unvested service-based and performance-based RSUs as of June 30, 2018 and changes during the six-month period then ended is as follows:


		Weighted
		Average Grant
Unvested Shares	Shares	Date Fair Value
Unvested at January 1, 2018	924,575	$	74.09
Granted(1)	474,715		84.26
Vested	(3,362)		71.72
Cancelled or forfeited	(13,318)		74.93
Unvested at June 30, 2018	1,382,610	$	77.58
Shares reserved for future grants (all plans)	1,368,824

⁽¹⁾

474,715 RSUs, including 178,970 performance-based RSUs, were granted in March 2018.

Accumulated Other Comprehensive Loss

Accumulated other comprehensive loss included the following:


			Pension and		Accumulated
	Foreign Currency		Postretirement		Other
	Translation		Benefit Adjustments,		Comprehensive
	Loss		Net of Tax		Loss
	(in millions)
Balance as of January 1, 2018	$	(51.1)	$	(20.5)	$	(71.6)
Current-period change		(14.1)		—		(14.1)
Balance as of June 30, 2018	$	(65.2)	$	(20.5)	$	(85.7)

Foreign currency translation adjustments have not been adjusted for income taxes. Pension and postretirement benefit adjustments are net of taxes of $13.6 million as of June 30, 2018 and December 31, 2017.