11. Stockholders' equity

Preferred stock

The Company is authorized to issue up to 15.0 million shares of preferred stock, $0.001 par value per share ("Preferred Stock"). Any Preferred Stock issued may have dividend rights, voting rights, conversion privileges, redemption characteristics, and sinking fund requirements as approved by the Company's board of directors.

Common stock

The Company currently has one class of common stock, $0.001 par value per share common stock ("Common Stock"), authorized and outstanding. The Company is authorized to issue up to 200.0 million shares of Common Stock. Holders of Common Stock are entitled to one vote for each share of Common Stock held on all matters, except as may be provided by law.

Stock options and restricted stock units

As of December 31, 2017, the Company had one equity award plan, the Fourth Amended and Restated Emergent BioSolutions Inc. 2006 Stock Incentive Plan (the "2006 Plan"), which includes both stock options and restricted stock units.

In connection with the Separation on August 1, 2016 and in accordance with the employee matters agreement and the Emergent Plans, the Company made certain adjustments to the exercise price and number of equity awards. Continuing Emergent employees with equity awards issued prior to Distribution received an equitable adjustment reflecting a revised exercise price and number of equity awards granted. Continuing Aptevo employees who had been granted Emergent equity awards had their grants canceled and reissued as Aptevo equity awards with an adjusted exercise price.

The following is a summary of stock option award activity under the 2006 Plan:

	2006 Plan
	Number of Shares			Weighted-Average Exercise Price		Aggregate Intrinsic Value
Outstanding at December 31, 2016		2,559,331		$	22.94	$	25,348,245
Granted		427,821			31.13
Exercised		(792,795	)		19.95
Forfeited		(72,952	)		29.30
Outstanding at December 31, 2017		2,121,405		$	25.48	$	44,518,585
Exercisable at December 31, 2017		1,307,330		$	22.63	$	31,170,967
Options expected to vest at December 31, 2017		632,954		$	29.91	$	10,480,716

The following is a summary of restricted stock unit award activity under the 2006 Plan:

	Number of Shares			Weighted-Average Grant Price		Aggregate Intrinsic Value
Outstanding at December 31, 2016		875,584		$	28.94	$	28,754,179
Granted		480,959			31.49
Vested		(423,840	)		30.52
Forfeited		(80,983	)		29.21
Outstanding at December 31, 2017		851,720		$	30.84	$	39,579,428

The weighted average remaining contractual term of options outstanding as of December 31, 2017 and 2016 was 4.0 years and 4.0 years, respectively. The weighted average remaining contractual term of options exercisable as of December 31, 2017 and 2016 was 3.2 years and 3.2 years, respectively.

The weighted average grant date fair value of options granted during the years ended December 31, 2017, 2016, and 2015 was $10.53, $9.24 and $8.66, respectively. The total intrinsic value of options exercised during the years ended December 31, 2017, 2016, and 2015 was $13.9 million, $15.6 million and $20.2 million, respectively. The total fair value of awards vested during 2017, 2016 and 2015 was $17.9 million, $16.9 million and $14.4 million, respectively. As of the year ended December 31, 2017, the total compensation cost and weighted average period over which total compensation is expected to be recognized related to unvested equity awards was $17.9 million and 2.0 years, respectively.

Stock-based compensation expense was recorded in the following financial statement line items:

	Year Ended December 31,
(in thousands)	2017		2016		2015
Cost of product sales	$	1,076	$	997	$	1,183
Research and development		2,526		2,297		2,324
Selling, general and administrative		11,611		14,062		11,234
Continuing operations		15,213		17,356		14,741
Discontinued operations		-		1,121		1,107
Total stock-based compensation expense	$	15,213	$	18,477	$	15,848

On July 14, 2016, the Company's board of directors authorized management to repurchase, from time to time, up to an aggregate of $50 million of the Company's common stock under a board-approved share repurchase program. The term of the board authorization of the repurchase program is until December 31, 2017. Any repurchased shares will be available for use in connection with the Company's stock plans and for other corporate purposes. During the year ended December 31, 2017, the Company has repurchased 0.8 million shares of common stock for $33.1 million.