Activity of stock options under the 2005 Plan, 2011 Plan and 2014 Plan (collectively, the "Plans") is set forth below:


	Number of Shares	Weighted-Average Exercise Price
Balance at December 31, 2020	1,020,978	$	23.38
Exercised	(42,408)	15.70
Canceled/Forfeited	—	—
Balance at March 31, 2021	978,570	23.71

Activity of unvested restricted stock awards and restricted stock units under the Plans during the three months ended March 31, 2021 is set forth below:


	Number of Shares	Weighted -Average Grant Date Fair Value
Unvested at December 31, 2020	369,629	$	163.03
Granted	53,080	255.00
Released/Vested - Restricted Stock/RSUs	(36,672)	140.42
Canceled/Forfeited	(4,182)	175.99
Unvested at March 31, 2021	381,855	177.84

As of March 31, 2021, 364,777 restricted stock awards and restricted stock units are expected to vest.

The following table sets forth the stock-based compensation expense included in the Company’s condensed consolidated statements of operations for the three months ended March 31, 2021 and 2020 (in thousands):


	Three Months Ended March 31,
	2021		2020
Cost of revenue	$	798	$	648
Research and development	1,062		874
Sales, general and administrative	4,535		4,167
Total	$	6,395	$	5,689

As of March 31, 2021, total unrecognized compensation cost was $55.6 million related to unvested share-based compensation arrangements which is expected to be recognized over a weighted average period of 2.9 years.

The total stock-based compensation cost capitalized in inventory was $1.3 million and $1.2 million as of March 31, 2021 and December 31, 2020, respectively.