Stock-Based Compensation

9 Months Ended

Sep. 30, 2019

Share-based Payment Arrangement, Noncash Expense [Abstract]

A summary of restricted and deferred stock transactions during the nine months ended September 30, 2019 is as follows:



	Number of shares
Non-vested stock awards outstanding at January 1, 2019	2,142,743
Awarded:
Time-vesting shares	381,145
Performance-based shares	202,876
Released:
Time-vesting shares	(130,044	)
Forfeitures:
Time-vesting shares	(97,275	)
Performance-based shares	(129,207	)
Non-vested stock awards outstanding at September 30, 2019	2,370,238

The performance-based share awards are subject to either a market condition or a performance condition. For awards subject to a market condition, the performance metric is the Company's total shareholder return, which includes share price appreciation and dividends paid during the three-year term of the award, measured against a peer group of companies. These awards cliff vest at the end of three years. The number of performance-based shares that will ultimately vest is based on the level of market performance achieved, ranging between 0% and 200% of the shares originally awarded, and are settled in stock.

For awards subject to a performance condition, the performance metric is the Company's average return on invested capital over the three-year term. These awards cliff vest at the end of three years. The number of performance-based shares that will ultimately vest is based on the level of performance achieved, ranging between 0% and 200% of the shares originally awarded, and are settled in stock.

The time-vesting restricted and deferred stock awards vest ratably over three to five years.

The weighted average grant-date fair values of awards issued during the nine months ended September 30, 2019 were $55.21 for the time-vesting stock awards and $46.08 for the performance-based stock awards.

The fair value of the performance-based shares subject to a market condition awarded in 2019 was calculated using a Monte Carlo valuation model, including a weighted average stock price volatility of 21.4%, an expected term of three years, and a weighted average risk-free interest rate of 2.45%.

As of September 30, 2019, unrecognized compensation cost related to outstanding non-vested stock awards was $68. The weighted average period over which the expense is expected to be recognized is 3.0 years. The aggregate market value of the shares released on the vesting dates was $7 for the nine months ended September 30, 2019.