Stock Based Compensation

3 Months Ended

Mar. 31, 2016

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock Based Compensation

Stock-Based Compensation

The Company’s 2003 Stock Incentive Plan, or the 2003 Plan, permits stock-based compensation awards to officers, directors, key employees and consultants. As of March 31, 2016, the 2003 Plan authorized grants of stock‑based compensation instruments to purchase or issue up to 19,686,565 shares of Company common stock, subject to adjustments provided by the 2003 Plan. As of March 31, 2016, there were 12,616,206 shares available for grant under the 2003 Plan.

Restricted stock amortization totaled $5.0 million, $3.8 million, and $3.1 million for the three months endedMarch 31, 2016, December 31, 2015 and March 31, 2015. Such amounts are included in "Compensation expense" on the condensed consolidated statements of earnings. The amount of unrecognized compensation expense related to unvested time-based restricted stock awards ("TRSAs") and performance-based restricted stock units ("PRSUs") as of March 31, 2016 totaled $51.8 million.

Time-Based Restricted Stock Awards

At March 31, 2016, there were 1,562,557 shares of unvested TRSAs outstanding. The TRSAs generally vest over a service period of three or four years from the date of the grant or immediately upon the death of an employee. Compensation expense related to TRSAs is based on the fair value of the underlying stock on the award date and is recognized over the vesting period using the straight‑line method.

Performance-Based Restricted Stock Units

At March 31, 2016, there were 153,715 shares of unvested PRSUs outstanding. The PRSUs will vest only if performance goals with respect to certain financial metrics are met over a three-year performance period. Compensation expense related to PRSUs is based on the fair value of the underlying stock on the award date and is amortized over the vesting period using the straight-line method unless it is determined that: (1) attainment of the financial metrics is less than probable, in which case a portion of the amortization is suspended, or (2) attainment of the financial metrics is improbable, in which case a portion of the previously recognized amortization is reversed and also suspended.