As of June 30, 2020, the Company was authorized to issue 205,000,000 total shares of capital stock, consisting of 200,000,000 shares of common stock and 5,000,000 shares of preferred stock. As of June 30, 2020, there were 64,300,599 shares of common stock outstanding, and the Company had reserved a total of 26,638,801 of its authorized shares of common stock for future issuance as follows:


			Shares Reserved for Future Issuance
Outstanding restricted stock units			3,534,193
Outstanding performance restricted stock units			1,831,648
Outstanding stock options			4,132,718
Reserved for convertible senior notes			17,140,242
Total shares of common stock reserved for future issuance			26,638,801

The Company maintains two stock-based compensation plans: the Amended and Restated 2014 Equity Incentive Plan (the “2014 Plan”) and the 2008 Stock Incentive Plan (the “2008 Plan” and together with the 2014 Plan, the “Stock Plans”). Upon the effective date of the 2014 Plan in January 2014, the Company ceased using the 2008 Plan to grant new equity awards. The shares available for future issuance under the 2014 Plan increased by 3,175,011 and 2,896,365 on January 1, 2020 and 2019, respectively, pursuant to the automatic share reserve increase provision in the 2014 Plan.

The Company also has a 2017 Employee Stock Purchase Plan (the “ESPP”). During the six months ended June 30, 2020, an aggregate of 83,573 shares of the Company’s common stock were purchased in accordance with the ESPP. Net proceeds from the issuance of these shares was $1.8 million. As of June 30, 2020, 729,391 shares remained available for purchase under the ESPP.

The following table presents stock-based compensation expense related to the Stock Plans and the ESPP, contained on the following line items on the Company’s condensed consolidated statements of operations and comprehensive loss for each of the periods indicated.


	Three Months Ended June 30,						Six Months Ended June 30,
	2020		2019		2020		2019
	(in thousands)
Curriculum and teaching	$	58	$	5	$	191	$	8
Servicing and support	3,642		1,834		7,570		3,503
Technology and content development	2,936		1,648		6,105		3,504
Marketing and sales	1,853		1,487		5,086		2,743
General and administrative	12,602		4,993		23,009		9,793
Total stock-based compensation expense	$	21,091	$	9,967	$	41,961	$	19,551

The 2014 Plan provides for the issuance of restricted stock units (“RSUs”) to employees and certain non-employees. RSUs generally vest over a three- or four-year period. The following table presents a summary of the Company’s RSU activity for the period indicated.


	Number of Units	Weighted- Average Grant Date Fair Value per Share
Outstanding balance as of December 31, 2019	2,281,142	$	40.49
Granted	1,865,348	20.11
Vested	(476,317)	52.61
Forfeited	(135,980)	32.13
Outstanding balance as of June 30, 2020	3,534,193	$	28.42

The 2014 Plan provides for the issuance of performance restricted stock units (“PRSUs”) to employees and certain non-employees. PRSUs generally include both service conditions and market conditions related to total shareholder return targets relative to that of companies comprising the Russell 3000 Index. The following table presents a summary of the Company’s PRSU activity for the period indicated.


	Number of Units	Weighted- Average Grant Date Fair Value per Share
Outstanding balance as of December 31, 2019	1,413,773	$	28.12
Granted	653,879	22.46
Vested	(444)	64.51
Forfeited	(235,560)	52.91
Outstanding balance as of June 30, 2020	1,831,648	$	22.90

The Stock Plans provide for the issuance of stock options to employees and certain non-employees. Stock options issued under the Stock Plans generally are exercisable for periods not to exceed 10 years and generally vest over four years. The following table presents a summary of the Company’s stock option activity for the period indicated.


	Number of Options	Weighted-Average Exercise Price per Share		Weighted-Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding balance as of December 31, 2019	4,373,895	$	34.24	5.88	$	28,736
Granted	8,597	19.61
Exercised	(195,728)	9.32
Forfeited	(22,294)	57.38
Expired	(31,752)	41.11
Outstanding balance as of June 30, 2020	4,132,718	35.22		5.54	58,683
Exercisable as of June 30, 2020	3,162,499	$	25.87	4.72	$	57,663

The weighted-average grant date fair value of stock options granted during the six months ended June 30, 2020 and 2019 was $11.48 and $32.71 per share, respectively.

The aggregate intrinsic value of stock options exercised during the six months ended June 30, 2020 and 2019 was $4.4 million and $13.2 million, respectively.

The total unrecognized compensation cost related to the unvested stock options as of June 30, 2020 was $26.5 million and will be recognized over a weighted-average period of approximately 2.60 years.