Stock-Based Compensation

In April 2010, the Company adopted an Omnibus Incentive Plan (the Incentive Plan) in order to provide an incentive to certain executive officers, personnel and directors. The Incentive Plan was amended and restated effective August 2011, increasing the number of shares issuable to 5,090,496. In March 2012, October 2013 and July 2014, additional shares of stock were reserved for issuance, bringing the total available shares issuable to 13,753,277. As of December 31, 2014, there were 11,855,060 shares of common stock reserved under the Incentive Plan, of which 6,416,163 shares remained available for future grants.

Stock Options

Stock options are awarded with an exercise price equal to the market price on the date of grant. The contractual terms for options expire ten years from the grant date and generally vest over a period of four years. The fair value of options on the date of grant is amortized on a straight-line basis over the requisite service period.

A summary of stock option activity under the Incentive Plan as of December 31, 2014 and 2013 and changes during the periods then ended are as follows:



	Number of Shares		Weighted-Average Price/Share			Weighted-Average Remaining Contractual Term	Aggregate Intrinsic Value
						(in years)
Outstanding at December 31, 2012	2,820,619		$	9.11		8.62	$	8,687
Granted	1,923,206		19.46
Exercised	(588,769	)	8.69
Cancelled	(844,292	)	(11.16		)
Outstanding at December 31, 2013	3,310,764		$	14.67		8.63	$	9,717
Granted	3,239,740		10.89
Exercised	(60,632	)	8.26
Cancelled	(1,050,975	)	(11.54		)
Outstanding at December 31, 2014	5,438,897		$	13.09		8.59	$	21



	Number of Shares	Weighted-Average Price/Share		Weighted-Average Remaining Contractual Term	Aggregate Intrinsic Value
				(in years)
Vested and Exercisable at December 31, 2013	894,813	$	9.38	7.61	$	5,358
Unvested at December 31, 2013	2,415,951	16.63		7.91
Vested and Exercisable at December 31, 2014	1,248,711	$	12.97	7.23	$	—
Unvested at December 31, 2014	4,190,186	13.13		9.04

The fair value of awards granted is estimated at the date of grant using the Black-Scholes option-pricing model with the following weighted-average assumptions:



Year of Grant	Risk-Free Interest Rate	Dividend Yield	Expected Term	Volatility Factor
			(in years)
2012	0.71%	0%	4.40	60.0%
2013	1.02%	0%	4.90	57.0%
2014	1.67%	0%	5.00	53.0%

Expected volatility is based on historical volatilities for publicly traded common stock of comparable peer companies over the estimated expected life of the stock options. The expected term represents the period of time the stock options are expected to be outstanding. The dividend yield assumption is based on the fact that the Company does not have a history of issuing dividends and does not anticipate issuing dividends in the near term. The risk-free interest rate is based on yields of U.S. Treasury securities with maturities similar to the estimated expected term of the stock options.

The weighted-average grant date fair value of options granted during 2014 and 2013 was $5.12 and $9.38 per share, respectively. The total intrinsic value of options exercised during 2014, 2013 and 2012 was $456, $7,376 and $297, respectively. The Company recognized stock-based compensation expense of $7,889, $4,064 and $2,943 in the consolidated statements of operations related to stock options in 2014, 2013 and 2012, respectively. As of December 31, 2014, total stock-based compensation expense related to non-vested options not yet recognized was $21,227, which will be recognized over the remaining weighted-average life of the awards, 2.87 years.