STOCKHOLDERS' EQUITY

Stock Based Compensation

Shares Available For Issuance

In the fiscal year ended December 31, 2016, we adopted the 2016 Incentive Plan (“2016 Plan”). Under the 2016 Plan, we may grant awards up to an aggregate amount of shares equal to the sum of: (i) 2,250 shares of Class A common stock (subject to adjustment in the event of stock splits and other similar events), plus (ii) such additional number of shares of Class A common stock (up to 2,723 shares) as is equal to the sum of the number of shares of Class A common stock that remained available for grant under the 2006 Stock Incentive Plan (“2006 Plan”) immediately prior to the expiration of the 2006 Plan and the number of shares of Class A common stock subject to awards granted under the 2006 Plan that expire, terminate or are otherwise surrendered, canceled, forfeited or repurchased by us. As of June 30, 2018, there were 1,620 Class A common stock equivalents available for future grant under the 2016 Plan.

Stock Options

Stock options are granted at a price equal to the prevailing fair value of our Class A common stock at the date of grant. Generally, stock options granted have a term not to exceed ten years and vest over a one year to four year period from the date of grant.

The fair value of each stock option granted, with the exception of market-based performance stock option grants, is estimated using a Black-Scholes option-pricing model, which requires extensive use of accounting judgment and financial estimation, including estimates of the expected term stock option holders will retain their vested stock options before exercising them and the estimated volatility of our Class A common stock price over the expected term. The fair value of each market-based performance stock option granted is estimated using a Monte Carlo option-pricing model, which also requires extensive use of accounting judgment and financial estimation, including estimates of the expected term stock option holders will retain their vested stock options before exercising them and the estimated volatility of our Class A common stock price over the expected term, but also including estimates of share price appreciation plus the value of dividends of our Class A common stock as compared to the Russell 2000 Index over the requisite service period.

A summary of stock option activity follows:



	Stock Options (1)		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (years)	Aggregate Intrinsic Value
Outstanding, December 31, 2017	727		$	5.82
Granted	—		$	—
Exercised	(83	)	$	4.80
Forfeited	—		$	—
Outstanding, June 30, 2018	644		$	5.95	6.0	$	12,651
Exercisable, June 30, 2018	444		$	4.81	5.2	$	9,228
Unvested, June 30, 2018	240		$	9.16	7.8	$	3,948


(1)	Market-based performance stock options are included at the 100% attainment level. Attainment of the maximum performance targets and market achievements would result in the issuance of an additional 40 shares of Class A common stock currently included in unvested.

Stock-based compensation expense for stock options was $126 and $250 during the three and six months ended June 30, 2018, respectively, as compared to $176 and $347 during the three and six months ended June 30, 2017, respectively.

During the three and six months ended June 30, 2018, the aggregate intrinsic value of stock options exercised was $403 and $1,556, respectively.

As of June 30, 2018, total unrecognized stock-based compensation expense related to outstanding stock options, including market-based performance stock options assuming the attainment of maximum performance targets, was $223, which will be recognized over a weighted average period of 0.3 years.

Other Stock Awards

Restricted stock awards, restricted stock units and performance stock units, with the exception of market-based performance stock units, are granted at a price equal to the fair value of our Class A common stock at the date of grant. The fair value of each market-based performance stock unit is estimated using a Monte Carlo pricing model, which requires extensive use of accounting judgment and financial estimation, including the estimated share price appreciation plus the value of dividends of our Class A common stock as compared to the Russell 2000 Index over the requisite service period.

Generally, restricted stock awards granted to non-employee directors vest incrementally over a three year period beginning on the first anniversary of the date of grant. Restricted stock units granted to non-employee directors typically vest in full on the first anniversary of the grant date. Restricted stock units granted to employees vest incrementally over an identified service period beginning on the grant date based on continued employment. Performance stock units granted to employees, including market-based performance stock units, vest at a future date following the grant date and are based on the attainment of performance targets and market achievements, as applicable.

A summary of restricted stock, restricted stock unit and performance stock unit activity follows:



	Restricted Stock, Restricted Stock Units, and Performance Stock Units (1)		Weighted Average Grant Date Fair Value		Weighted Average Remaining Contractual Term (years)	Aggregate Intrinsic Value
Outstanding, December 31, 2017	1,091		$	9.81
Granted	225		$	24.85
Class A Common Stock Vested	(370	)	$	6.91
Forfeited	(3	)	$	9.11
Outstanding, June 30, 2018	943		$	14.53	1.4	$	10,492
Unvested, June 30, 2018	1,393		$	14.73	1.3	$	15,237


(1)	Market-based performance stock unit grants are included at the 100% attainment level. Attainment of the maximum performance targets and market achievements would result in the issuance of an additional 450 shares of Class A common stock currently included in unvested.

Stock-based compensation expense related to restricted stock, restricted stock units and performance stock units was $1,946 and $3,876 during the three and six months ended June 30, 2018, respectively, as compared to $1,441 and $2,499 during the three and six months ended June 30, 2017, respectively.

During the three and six months ended June 30, 2018, the total fair value of other stock awards vested was $742 and $9,616, respectively.

As of June 30, 2018, total unrecognized stock-based compensation expense related to outstanding restricted stock and restricted stock units was $4,316, which will be recognized over a weighted average period of 1.5 years. As of June 30, 2018, maximum unrecognized stock-based compensation expense related to outstanding performance stock units, assuming the attainment of maximum performance targets, was $7,016 to be recognized over a weighted average period of 1.3 years.

The weighted average fair value of market-based performance stock units granted during the six months ended June 30, 2018 was $26.02 per award, which was calculated using a Monte Carlo pricing model assuming a risk free interest rate of 2.39% and an expected volatility of 32.70% assuming no expected dividend yield. The risk-free interest rate is based on the U.S. Treasury yield curve for the expected service period of the award. Expected volatility is calculated using the daily volatility of our Class A common stock over the expected service period of the award.

The Monte Carlo pricing model requires extensive use of accounting judgment and financial estimation. Application of alternative assumptions could produce significantly different estimates of the fair value of stock-based compensation and consequently, the related amounts recognized in the consolidated statements of operations.

We also recorded $48 and $71 of stock-based compensation expense related to our Amended and Restated 1997 Employee Stock Purchase Plan during the three and six months ended June 30, 2018, respectively, as compared to $37 and $65 during the three and six months ended June 30, 2017, respectively.

Accumulated Other Comprehensive Income

A summary of the changes in the balances of each component of accumulated other comprehensive income, net of tax follows:




	Marketable Securities			Interest Rate Swaps
Balance, December 31, 2017	$	18		$	166
Cumulative effect of new accounting principle	(18		)	—
Other comprehensive income before reclassifications	—			570
Amounts reclassified from accumulated other comprehensive income	—			91
Income tax expense related to items of other comprehensive income	—			(178		)
Net current-period other comprehensive income	—			483
Balance, June 30, 2018	$	—		$	649

A summary of reclassifications out of accumulated other comprehensive income, net of tax follows:



	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Details About Accumulated Other Comprehensive Income Components	Amounts Reclassified Out of Accumulated Other Comprehensive Income								Affected Line Item in the Consolidated Statements of Operations
Interest rate swaps	$	38	$	138	$	91	$	208	Interest expense
	38		138		91		208		Income (loss) before income taxes
	—		—		—		—		Provision (benefit) for income taxes
	$	38	$	138	$	91	$	208	Net income (loss)