STOCK AWARD PLANS

Stock-based compensation cost is measured at the grant date based on the value of the award and is recognized as expense as it vests. A summary of our total compensation expense recognized in our condensed consolidated statements of operations and comprehensive income for stock-based compensation is as follows (in thousands):



	Three Months Ended March 31,
	2016		2015
Stock options	$	3,337	$	3,764
Stock awards	10,840		10,679
Company expense on ESPP discount	1,002		893
Total stock-based compensation expense	$	15,179	$	15,336

On May 9, 2013, our shareholders approved our 2013 Equity Incentive Plan, which allows us to grant certain stock awards, including stock options at fair market value and performance shares and restricted stock units, to our key employees and outside directors. A maximum of 3,400,000 shares plus the shares remaining available for future grants under the 1997 Plan as of May 9, 2013, can be granted under this plan. Approximately 728,188 shares were available for stock awards as of March 31, 2016. Shares subject to awards that expire or are canceled without delivery of shares or that are settled in cash generally become available again for issuance under the plan.

Stock Options - We have awarded performance-based stock options to certain key employees. These options are subject to certain vesting requirements over a five-year period based on the company’s earnings growth. Any options remaining unvested at the end of the five-year vesting period are forfeited to the company. Although participants can exercise options via a stock swap exercise, we do not issue reloads (restoration options).

The fair value of these options is established based on the market price on the date of grant, discounted for post-vesting holding restrictions, calculated using the Black-Scholes option pricing model. Changes in measured stock price volatility and interest rates are the primary reasons for changes in the discount. These grants are being expensed based on the terms of the awards. As of March 31, 2016, unrecognized compensation expense related to stock options was $50.8 million. The amount of future expense to be recognized will be based on the company’s earnings growth and certain other conditions.

Full Value Awards - We have awarded performance shares and restricted stock units to certain key employees and non-employee directors. These awards are subject to certain vesting requirements over a five-year period, based on the company’s earnings growth. The awards also contain restrictions on the awardees’ ability to sell or transfer vested awards for a specified period of time. The fair value of these awards is established based on the market price on the date of grant, discounted for post-vesting holding restrictions. The discounts on outstanding grants vary from 17 percent to 22 percent and are calculated using the Black-Scholes option pricing model-protective put method. Changes in measured stock price volatility and interest rates are the primary reasons for changes in the discount. These grants are being expensed based on the terms of the awards.

We have also awarded restricted shares and restricted stock units to certain key employees that vest primarily based on their continued employment. The value of these awards is established by the market price on the date of the grant and is being expensed over the vesting period of the award.

We have also issued to certain key employees and non-employee directors restricted stock units which are fully vested upon issuance. These units contain restrictions on the awardees’ ability to sell or transfer vested units for a specified period of time. The fair value of these units is established using the same method discussed above. These grants have been expensed during the year they were earned.

As of March 31, 2016, there was unrecognized compensation expense of $116.2 million related to previously granted full value awards. The amount of future expense to be recognized will be based on the company’s earnings growth and certain other conditions.

Employee Stock Purchase Plan - Our 1997 Employee Stock Purchase Plan allows our employees to contribute up to $10,000 of their annual cash compensation to purchase company stock. Purchase price is determined using the closing price on the last day of each quarter discounted by 15 percent. Shares vest immediately. The following is a summary of the employee stock purchase plan activity (dollar amounts in thousands):



Three Months Ended March 31, 2016
Shares purchased by employees	Aggregate cost to employees	Expense recognized by the company
89,978	$5,677	$1,002