As of June 30, 2020, there were 2,794,893 shares and 2,341,331 shares available for grant under The Hanover Insurance Group 2014 Long-Term Incentive Plan and The Hanover Insurance Group 2014 Employee Stock Purchase Plan, respectively.

Compensation cost for the Company’s stock-based awards and the related tax benefits were as follows:

	Three Months Ended June 30,						Six Months Ended June 30,
(in millions)	2020			2019			2020			2019
Stock-based compensation expense	$	4.5		$	4.4		$	9.5		$	8.6
Tax benefit		(0.9	)		(0.9	)		(2.0	)		(1.8	)
Stock-based compensation expense, net of taxes	$	3.6		$	3.5		$	7.5		$	6.8

Information on the Company’s stock option activity for the six months ended June 30, 2020 and 2019 is summarized below.

	Six Months Ended June 30,
	2020					2019
(in whole shares and dollars)	Shares			Weighted Average Exercise Price		Shares			Weighted Average Exercise Price
Outstanding, beginning of period		1,121,559		$	87.88		1,099,076		$	85.75
Granted		242,598			118.34		232,568			95.05
Exercised		(40,889	)		77.86		(127,830	)		72.79
Forfeited or cancelled		(21,862	)		111.65		(19,203	)		101.20
Outstanding, end of period		1,301,406			93.47		1,184,611			88.72

The Company currently issues time-based, market-based and performance-based restricted stock units to eligible employees, all of which generally vest after 3 years of continued employment.

The following tables summarize activity information about employee restricted stock units:

	Six Months Ended June 30,
	2020					2019
(in whole shares and dollars)	Shares			Weighted Average Grant Date Fair Value		Shares			Weighted Average Grant Date Fair Value
Time-based restricted stock units:
Outstanding, beginning of period		335,166		$	109.55		332,481		$	97.28
Granted		142,412			117.72		145,040			117.55
Vested		(85,880	)		91.98		(106,864	)		83.87
Forfeited		(17,004	)		116.00		(20,404	)		101.71
Outstanding, end of period		374,694			116.39		350,253			109.51
Performance-based and market-based restricted stock units:
Outstanding, beginning of period		86,252		$	110.70		69,838		$	95.58
Granted		54,415			105.10		42,119			117.09
Vested		(40,601	)		80.92		(14,118	)		84.39
Forfeited		(3,023	)		124.78	—			—
Outstanding, end of period		97,043			119.59		97,839			106.45

In the first six months of 2020 and 2019, the Company granted market-based awards totaling 34,911 and 23,924, respectively, to certain members of senior management, which are included in the table above as performance and market-based restricted stock activity. The vesting of these stock units is based on the relative total shareholder return (“TSR”) of the Company. This metric is generally based on relative TSR for a three-year period as compared to a pre-selected group of property and casualty companies. The fair value of market-based awards was estimated at the date of grant using a valuation model. These units have the potential to range from 0% to 150% of the shares disclosed. Included in the amount granted above in 2020 and 2019 are 13,532 shares and 5,820 shares, respectively, related to market-based awards that achieved a payout in excess of 100%. These awards vested in the first quarters of 2020 and 2019, respectively.

The Company also granted performance-based restricted stock units in 2020 and 2019, totaling 19,504 and 18,195, respectively, which are based upon the Company’s achievement of return on equity objectives. These units have the potential to range from 0% to 150% of the shares disclosed, which varies based on grant year and individual participation level. Increases above the 100% target level are reflected as granted in the period in which performance-based stock unit goals are achieved. Decreases below the 100% target level are reflected as forfeited. There were no performance-based awards that vested in 2020 or 2019.