9. Stockholders’ Equity

We recorded stock-based expense related to grants of employee and consultant stock options, restricted stock and restricted stock units (“ZSUs”) in our consolidated statements of operations as follows (in thousands):

	Three Months Ended March 31,
	2017		2016
Cost of revenue	$	619	$	649
Research and development		11,713		24,203
Sales and marketing		1,787		1,991
General and administrative		3,407		2,765
Total stock-based expense	$	17,526	$	29,608

The following table shows stock option activity for the first quarter of 2017 (in thousands, except weighted-average exercise price and weighted-average contractual term):

	Outstanding Options
				Weighted-		Aggregate		Weighted-
				Average		Intrinsic Value of		Average
				Exercise		Stock Options		Contractual Term
	Stock Options			Price		Outstanding		(in years)
Balance as of December 31, 2016		36,858		$	2.08	$	26,411		6.81
Granted		—			—
Forfeited and cancelled		(591	)		3.74
Exercised		(957	)		0.64
Balance as of March 31, 2017		35,310		$	2.09	$	30,240		6.47

The following table shows a summary of ZSU activity for the first quarter of 2017 (in thousands, except weighted-average grant date fair value):

	Outstanding ZSUs
				Weighted-		Aggregate
				Average Grant Date		Intrinsic Value of
	Shares			Fair Value		Unvested ZSUs
Unvested as of December 31, 2016		59,452		$	2.66	$	152,792
Granted		4,016			2.80
Vested		(4,236	)		2.79
Forfeited and cancelled		(7,824	)		2.45
Unvested as of March 31, 2017		51,408		$	2.69	$	146,513

The following table shows a summary of changes in accumulated other comprehensive income by component for the first quarter of 2017 (in thousands):

	Foreign Currency Translation			Unrealized Gains (Losses) on Available-for-Sale Securities			Total
Balance as of December 31, 2016	$	(128,671	)	$	(23	)	$	(128,694	)
Other comprehensive income (loss) before reclassifications		5,481			23			5,504
Net current-period other comprehensive income (loss)		5,481			23			5,504
Balance as of March 31, 2017	$	(123,190	)	$	—		$	(123,190	)

In November 2016, we announced that our Board Directors authorized a share repurchase program allowing us to repurchase up to $200 million of our outstanding shares of Class A common stock (“2016 Share Repurchase Program”). In the first quarter of 2017, we repurchased 31.2 million shares of our Class A common stock under the 2016 Share Repurchase Program at a weighted average price of $2.70 per share for a total of $84.5 million. As of March 31, 2017, in the aggregate, we repurchased 43.6 million shares under the 2016 Share Repurchase Program at an average price of $2.72 per share for a total of $118.7 million.