The Company’s 2013 Equity Plan authorizes the issuance of various types of share-based awards to the Company’s employees, officers, directors, and other eligible participants. As of March 31, 2021, a total of 2,300,000 shares of the Company’s class A common stock were authorized for issuance under the 2013 Equity Plan. As of March 31, 2021, there were 115,138 shares of class A common stock reserved and available for future issuance under the 2013 Equity Plan. In April 2021, the Board of Directors authorized, subject to stockholder approval, an increase in the total number of shares of the Company’s class A common stock authorized for issuance under the 2013 Equity Plan from 2,300,000 shares to 2,750,000 shares.

As of March 31, 2021, there were options to purchase 1,273,304 shares of class A common stock outstanding under the 2013 Equity Plan.

The following table summarizes the Company’s stock option activity (in thousands, except per share data and years) for the three months ended March 31, 2021:

	Stock Options Outstanding
				Weighted Average		Aggregate		Weighted Average
				Exercise Price		Intrinsic		Remaining Contractual
	Shares			Per Share		Value		Term (Years)
Balance as of January 1, 2021		1,157		$	139.48
Granted		280		$	691.93
Exercised		(159	)	$	150.43	$	98,332
Forfeited/Expired		(5	)	$	138.82
Balance as of March 31, 2021		1,273		$	259.39
Exercisable as of March 31, 2021		564		$	132.02	$	308,274		3.9
Expected to vest as of March 31, 2021		709		$	360.60	$	229,435		9.0
Total		1,273		$	259.39	$	537,709		6.7

Stock options outstanding as of March 31, 2021 are comprised of the following range of exercise prices per share (in thousands, except per share data and years):

	Stock Options Outstanding at March 31, 2021
			Weighted Average		Weighted Average
			Exercise Price		Remaining Contractual
Range of Exercise Prices per Share	Shares		Per Share		Term (Years)
$121.43 - $200.00		994	$	137.74		5.8
$600.01 - $700.00		276	$	691.23		9.9
$700.01 - $756.55		3	$	756.55		9.9
Total		1,273	$	259.39		6.7

An aggregate of 78,125 stock options with an aggregate grant date fair value of $4.5 million vested during the three months ended March 31, 2021. The weighted average grant date fair value of stock option awards using the Black-Scholes pricing model was $381.26 for each share subject to a stock option granted during the three months ended March 31, 2021 based on the following assumptions:

No stock option awards were granted during the three months ended March 31, 2020.

For the three months ended March 31, 2021 and 2020, the Company recognized approximately $5.3 million and $3.2 million, respectively, in share-based compensation expense from stock options granted under the 2013 Equity Plan. As of March 31, 2021, there was approximately $122.9 million of total unrecognized share-based compensation expense related to unvested stock options. The Company expects to recognize this remaining share-based compensation expense over a weighted average vesting period of approximately 3.7 years.

As of March 31, 2021, there were 90,100 restricted stock units outstanding under the 2013 Equity Plan, which the Company intends to settle in shares. The following table summarizes the Company’s restricted stock unit activity (in thousands) for the periods indicated:

	Restricted Stock Units Outstanding
				Aggregate
				Intrinsic
	Units			Value
Balance as of January 1, 2021		74
Granted		17
Vested		0		$	0
Forfeited		(1	)
Balance as of March 31, 2021		90
Expected to vest as of March 31, 2021		90		$	61,160

No restricted stock units vested during the three months ended March 31, 2021. The weighted average grant date fair value of restricted stock units granted during the three months ended March 31, 2021 was $691.99 based on the fair value of the Company’s class A common stock. The Company recognized approximately $1.2 million in share-based compensation expense for the three months ended March 31, 2021 from restricted stock units granted under the 2013 Equity Plan. As of March 31, 2021, there was approximately $24.2 million of total unrecognized share-based compensation expense related to unvested restricted stock units. As of March 31, 2021, the Company expects to recognize this remaining share-based compensation expense over a weighted average vesting period of approximately 3.8 years.

During the three months ended March 31, 2021, the Company granted 9,000 “other stock-based awards” under the 2013 Equity Plan. As of March 31, 2021, there were a total of 14,000 other stock-based awards outstanding under the 2013 Equity Plan. These other stock-based awards are similar to stock options, except these awards are settled in cash only and not in shares of the Company’s class A common stock.

During the three months ended March 31, 2021, the Company also granted 900 restricted stock units under the 2013 Equity Plan that can only be settled in cash. As of March 31, 2021, there were a total of 900 cash-settled restricted stock units outstanding under the 2013 Equity Plan. These cash-settled restricted stock units are similar to the Company’s other restricted stock units, except they are settled in cash only and not in shares of the Company’s class A common stock.

Both the other stock-based awards and the cash-settled restricted stock units are classified as liabilities in the Company’s Consolidated Balance Sheets due to the required cash settlement feature and the fair value of the awards is remeasured each quarterly reporting period. For the three months ended March 31, 2021, the Company recognized $0.9 million in share-based compensation expense from other stock-based awards and cash-settled restricted stock units. During the three months ended March 31, 2020, share-based compensation expense from other stock-based awards was not material. As of March 31, 2021, there was approximately $5.4 million of total unrecognized share-based compensation expense related to other stock-based awards and cash-settled restricted stock units. The Company expects to recognize this remaining share-based compensation expense over a weighted average vesting period of approximately 3.0 years, subject to additional fair value adjustments through the earlier of settlement or expiration.

During the first quarter of 2021, the Company adopted the 2021 ESPP. The purpose of the 2021 ESPP is to provide eligible employees of the Company and certain of its subsidiaries with opportunities to purchase shares of the Company’s class A common stock, commencing at such time and on such dates as the Board of Directors of the Company shall determine. An aggregate of 100,000 shares of the Company’s class A common stock has been authorized for issuance under the 2021 ESPP.

Unless otherwise determined by the Board of Directors, shares are purchased at a price equal to 85% of the lesser of the closing price of the Company’s class A common stock on the first or last business day of the offering period, respectively. Share-based compensation expense is based on the grant date fair value, which consists of the intrinsic value of the 15% discounted share purchase rights and the fair value of the look-back provision using the Black-Scholes valuation model, recognized on a straight-line basis over the offering period. The grant date is the offering period commencement date.

The first offering period under the 2021 ESPP commenced on February 16, 2021 and will end on August 15, 2021. During the three months ended March 31, 2021, the Company recognized approximately $0.4 million in share-based compensation expense related to the 2021 ESPP. As of March 31, 2021, there was approximately $1.3 million of total unrecognized share-based compensation expense related to the 2021 ESPP. The Company expects to recognize this remaining share-based compensation expense over a period of approximately 0.4 years. As of March 31, 2021, no shares have been issued in connection with the 2021 ESPP.