7. Stock-Based Compensation

The Company provides equity-based compensation awards to employees, independent contractors and directors as an effective means for attracting, retaining and motivating such individuals. The Company maintains two share-based compensation plans: the 2014 Equity Incentive Plan (the “2014 Plan”) and the 2008 Stock Incentive Plan (the “2008 Plan”). Upon the effective date of the 2014 Plan in January 2014, the Company ceased using the 2008 Plan to grant new equity awards and began using the 2014 Plan for grants of new equity awards.

The number of shares of the Company’s common stock that may be issued under the 2014 Plan will automatically increase on January 1st of each year, for a period of ten years, from January 1, 2015 continuing through January 1, 2024, by 5% of the total number of shares of the Company’s common stock outstanding on December 31st of the preceding calendar year, or a lesser number of shares as may be determined by the Company’s board of directors. The shares available for issuance increased by 2,288,820 and 2,036,503 on January 1, 2016 and 2015, respectively, pursuant to the automatic share reserve increase provision under the 2014 Plan.

Stock-Based Compensation Expense

Stock-based compensation expense related to stock-based awards is included in the following line items in the accompanying condensed consolidated statements of operations:

	Three Months Ended June 30,				Six Months Ended June 30,
	2016		2015		2016		2015
	(in thousands)
Servicing and support	$	923	$	607	$	1,574	$	995
Technology and content development	654		427		1,106		658
Program marketing and sales	355		277		613		459
General and administrative	2,044		2,556		4,227		3,803

Total stock-based compensation expense	$	3,976	$	3,867	$	7,520	$	5,915

Stock Options

The following table summarizes the assumptions used for estimating the fair value of the stock options granted for the periods presented.

	Three Months Ended June 30,		Six Months Ended June 30,
	2016	2015	2016	2015
Risk-free interest rate	1.3% – 1.4%	1.5 – 1.9%	1.3% – 1.9%	1.5% – 1.9%
Expected term (years)	5.75 – 6.08	6.00 – 6.08	5.75 – 6.08	5.83 – 6.08
Expected volatility	50%	50%	50%	50%
Dividend yield	0%	0%	0%	0%
Weighted-average grant date fair value per share	$11.01	$12.51	$11.02	$12.42

The following is a summary of the stock option activity for the six months ended June 30, 2016:

	Number of Options		Weighted-Average Exercise Price per Share		Weighted-Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding balance at December 31, 2015	5,298,510		$	8.07	6.66	$	105,595
Granted	712,286		22.72		9.56
Exercised	(509,878	)	4.27		1.61
Forfeited	(142,736	)	19.99

Outstanding balance at June 30, 2016	5,358,182		10.06		6.59	103,716

Exercisable at June 30, 2016	3,534,756		5.85		5.56	83,290

Vested and expected to vest at June 30, 2016	5,197,319		9.73		6.52	102,306

The total compensation cost related to the nonvested options not yet recognized as of June 30, 2016 was $14.3 million and will be recognized over a weighted-average period of approximately 2.3 years.

The aggregate intrinsic value of the options exercised during the six months ended June 30, 2016 and 2015 was $10.5 million and $14.0 million, respectively.

Restricted Stock Units

The following is a summary of restricted stock unit activity for the three months ended June 30, 2016:

	Number of Restricted Stock Units		Weighted- Average Grant Date Fair Value
Outstanding balance at December 31, 2015	1,220,008		$	17.97
Granted	665,084		22.75
Vested	(350,681	)	16.76
Forfeited	(113,039	)	20.05

Outstanding balance at June 30, 2016	1,421,372		20.34

The total compensation cost related to the nonvested restricted stock units not yet recognized as of June 30, 2016 was $22.5 million and will be recognized over a weighted-average period of approximately 2.8 years.