(3) Share-based Compensation

During the three‑month periods ended June 30, 2018 and 2017, the Company recognized share-based compensation expense of $5.2 million and $11.7 million, respectively. During the six‑month periods ended June 30, 2018 and 2017, the Company recognized share-based compensation expense of $11.1 million and $19.6 million, respectively. Activity in options and restricted stock during the six-month period ended June 30, 2018 and related balances outstanding as of that date are reflected below. The weighted average fair value per share of options granted to employees for the three-month periods ended June 30, 2018 and 2017 were approximately $14.32 and $7.24, respectively The weighted average fair value per share of options granted to employees for the six-month periods ended June 30, 2018 and 2017 were approximately $12.84 and $10.75, respectively.

The following table summarizes share-based compensation expense included within the consolidated statements of operations:

	For the three-month period ended June 30,				For the six-month period ended June 30,
(In millions)	2018		2017		2018		2017
Research and development expense	$	1.5	$	3.8	$	3.2	$	6.4
Selling, general and administrative expense		3.7		7.9		7.9		13.2
Total	$	5.2	$	11.7	$	11.1	$	19.6

A summary of share-based compensation activity for the six-month period ended June 30, 2018 is presented below:

Stock Option Activity

	Number of Shares (In thousands)			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Intrinsic Value (In thousands)
Balance at January 1, 2018		8,930		$	29.46
Granted		705			25.12
Cancelled		(401	)		27.26
Exercised		(638	)		21.18
Balance at June 30, 2018		8,596		$	29.82		5.9	$	19,315
Vested and expected to vest at June 30, 2018		8,545		$	29.85		5.9	$	19,096
Vested and exercisable at June 30, 2018		6,669		$	30.51		5.1	$	13,284

Restricted Stock and Performance Stock Unit Activity

(In thousands)
Restricted Stock and Performance Stock Units	Number of Shares
Nonvested at January 1, 2018		697
Granted		—
Vested		(143	)
Forfeited		(106	)
Nonvested at June 30, 2018		448

Unrecognized compensation cost for unvested stock options, restricted stock awards and performance stock units as of June 30, 2018 totaled $30.3 million and is expected to be recognized over a weighted average period of approximately 1.8 years.

During the three‑month period ended June 30, 2018, the Company repurchased 16,339 shares of common stock at an average price of $23.58 per share or approximately $0.4 million. During the six‑month period ended June 30, 2018, the Company repurchased 63,124 shares of common stock at an average price of $25.15 per share or approximately $1.6 million. The share repurchase consists primarily of common stock withheld to cover the tax liability in connection with the settlement of vested restricted stock units and stock options that were exercised in the three and six-month period ended June 30, 2018.