Stock-Based Compensation | Stock-Based Compensation Our 2004 Equity Incentive Plan (the "2004 Plan") authorizes the granting of options to purchase shares of our Class B common stock, restricted stock units ("RSUs") and other stock-based awards to our employees, consultants, officers and directors. Our 2013 Equity Incentive Plan (the "2013 Plan" and, together with the 2004 Plan, the "Plans"), which was a successor to our 2004 Plan, authorizes the granting of options to purchase shares of our Class A common stock, RSUs and other stock-based awards to our employees, consultants, officers and directors. Options granted under the Plans may be incentive or nonstatutory stock options. Incentive stock options may only be granted to employees. The term of each option is stated in the award agreement, but shall be no more than ten years from the date of grant. Options typically vest over a period of four years. A summary of the option activity under the Plans during the six months ended June 30, 2015 is presented below: Options Outstanding Shares Weighted Average Exercise Price Per Share Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (in years) (in thousands) Balances at December 31, 2014 8,515,879 $ 8.76 Options exercised (1,555,909 ) 8.29 Options canceled (10 ) 9.30 Options forfeited (56,715 ) 16.13 Balances at June 30, 2015 6,903,245 $ 8.81 6.51 $ 735,146 Vested and expected to vest at June 30, 2015 6,853,506 $ 8.76 6.50 $ 730,143 Exercisable at June 30, 2015 4,510,114 $ 7.16 6.06 $ 487,705 RSUs entitle the holder to receive shares of Class A common stock as the award vests. RSUs typically vest over a period of four years. The fair value of an RSU is determined by using the closing price of our Class A common stock as reported on the New York Stock Exchange on the date of grant. The Company's non-vested RSUs do not have nonforfeitable rights to dividends or dividend equivalents. A summary of the RSU activity under the 2013 Plan during the six months ended June 30, 2015 is presented below: Number of Shares Underlying Outstanding RSUs Weighted-Average Grant-Date Fair Value per RSU Non-Vested outstanding at December 31, 2014 2,818,661 $ 77.77 RSUs granted 2,041,106 102.12 RSUs vested (357,242 ) 82.42 RSUs forfeited (79,987 ) 82.48 Non-Vested outstanding at June 30, 2015 4,422,538 $ 88.54 Stock-based compensation expense is amortized using the straight-line method over the requisite service period. As of June 30, 2015 , total unrecognized compensation expense, adjusted for estimated forfeitures, related to stock options and non-vested RSUs was approximately $344.4 million which is expected to be recognized over a period of 3.2 years . The summary of shares available for issuance of equity based awards (including stock options and RSUs) during the six months ended June 30, 2015 is as follows: Shares Available for Grant Balance at December 31, 2014 6,229,892 Authorized 3,493,410 Granted (2,041,106 ) Canceled 10 Forfeited 136,702 Balance at June 30, 2015 7,818,908 |