We recognized share-based payment expense of $19,524 and $17,787 for the three months ended June 30, 2015 and 2014, respectively, and $38,941 and $36,027 for the six months ended June 30, 2015 and 2014, respectively.

2015 Long-Term Stock Incentive Plan

In May 2015, our stockholders approved the Sirius XM Holdings Inc. 2015 Long-Term Stock Incentive Plan (the “2015 Plan”).  Employees, consultants and members of our board of directors are eligible to receive awards under the 2015 Plan.  The 2015 Plan provides for the grant of stock options, restricted stock awards, restricted stock units and other stock-based awards that the compensation committee of our board of directors may deem appropriate.  Vesting and other terms of stock-based awards are set forth in the agreements with the individuals receiving the awards.  Stock-based awards granted under the 2015 Plan are generally subject to a vesting requirement.  Stock options generally expire ten years from the date of grant.  Each restricted stock unit entitles the holder to receive one share of common stock upon vesting.  As of June 30, 2015, 393,554 shares of common stock were available for future grants under the 2015 Plan.

Other Plans

We maintain four other share-based benefit plans — the Sirius XM Radio Inc. 2009 Long-Term Stock Incentive Plan, the XM 2007 Stock Incentive Plan, the Amended and Restated Sirius Satellite Radio 2003 Long-Term Stock Incentive Plan and the XM 1998 Shares Award Plan. No further awards may be made under these plans.  

The following table summarizes the weighted-average assumptions used to compute the fair value of options granted to employees and members of our board of directors:

There were no options granted to third parties during the three and six months ended June 30, 2015 and 2014.  We do not intend to pay regular dividends on our common stock.  Accordingly, the dividend yield percentage used in the Black-Scholes-Merton option value was zero for all periods.

The following table summarizes stock option activity under our share-based plans for the six months ended June 30, 2015:

The weighted average grant date fair value per share of options granted during the six months ended June 30, 2015 and 2014 was $0.84 and $1.09, respectively.  The total intrinsic value of stock options exercised during the six months ended June 30, 2015 and 2014 was $39,795 and $20,435, respectively.  During the six months ended June 30, 2015, the number of shares which were issued as a result of stock option exercises was 6,249.

We recognized share-based payment expense associated with stock options of $16,553 and $16,193 for the three months ended June 30, 2015 and 2014, respectively, and $33,244 and $32,808 for the six months ended June 30, 2015 and 2014, respectively.

The following table summarizes the nonvested restricted stock unit activity and stock awards granted under our share-based plans for the six months ended June 30, 2015:

The weighted average grant date fair value per share of restricted stock units and stock awards granted during the six months ended June 30, 2015 and 2014 was $3.88 and $3.70, respectively.  The total intrinsic value of the 77 stock awards vesting during the six months ended June 30, 2015 was $300.

We recognized share-based payment expense associated with restricted stock units and stock awards of $2,971 and $1,594 during the three months ended June 30, 2015 and 2014, respectively, and $5,697 and $3,219 during the six months ended June 30, 2015 and 2014, respectively.

Total unrecognized compensation costs related to unvested share-based payment awards for stock options and restricted stock units granted to employees and members of our board of directors at June 30, 2015 and December 31, 2014, net of estimated forfeitures, were $129,822 and $162,985, respectively.  The total unrecognized compensation costs at June 30, 2015 are expected to be recognized over a weighted-average period of 2.5 years.

401(k) Savings Plan

Sirius XM sponsors the Sirius XM Radio Inc. 401(k) Savings Plan (the “Sirius XM Plan”) for eligible employees. The Sirius XM Plan allows eligible employees to voluntarily contribute from 1% to 50% of their pre-tax eligible earnings, subject to certain defined limits. We match 50% of an employee’s voluntary contributions per pay period on the first 6% of an employee’s pre-tax salary up to a maximum of 3% of eligible compensation.  Employer matching contributions under the Sirius XM Plan vest at a rate of 33.33% for each year of employment and are fully vested after three years of employment for all current and future contributions.  Beginning in January 2014, our cash employer matching contributions were no longer used to purchase shares of our common stock on the open market, unless the employee elects our common stock as their investment option for this contribution.  We contributed $1,513 and $1,254 during three months ended June 30, 2015 and 2014, respectively, and $4,540 and $3,133 during the six months ended June 30, 2015 and 2014, respectively, to the Sirius XM Plan in fulfillment of our matching obligation.

Sirius XM Holdings Inc. Deferred Compensation Plan

In June 2015, we adopted the Sirius XM Holdings Inc. Deferred Compensation Plan (the “DCP”), effective July 1, 2015.  The DCP allows members of our Board of Directors and certain eligible employees to defer all or a portion of their base salary, cash incentive compensation and/or Board of Directors compensation, as applicable, each plan year.  Pursuant to the terms of the DCP, we may elect to make additional contributions beyond amounts deferred by participants, but we are under no obligation to do so.  The Company intends to establish a grantor (or “rabbi”) trust to facilitate the payment of obligations under the DCP.  As of June 30, 2015, there were no balances or amounts associated with the DCP that were recorded in our unaudited consolidated financial statements (as the DCP was not yet effective).