Stock-Based Compensation

6 Months Ended

Jun. 30, 2020

Share-based Payment Arrangement, Noncash Expense [Abstract]

A summary of restricted and deferred stock transactions during the six months ended June 30, 2020 is as follows:


			Number of shares
Non-vested stock awards outstanding at January 1, 2020			2,102,654
Awarded:
Time-vesting shares			275,173
Performance-based shares			166,018
Released:
Time-vesting shares			(140,987)
Performance-based shares			(181,705)
Forfeitures:
Time-vesting shares			(56,566)
Performance-based shares			(7,651)
Non-vested stock awards outstanding at June 30, 2020			2,156,936

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 six months ended June 30, 2020 were $69.71 for the time-vesting stock awards and $72.08 for the performance-based stock awards.

The fair value of the performance-based shares subject to a market condition awarded in 2020 was calculated using a Monte Carlo valuation model, including a weighted average stock price volatility of 22.0%, an expected term of three years, and a weighted average risk-free interest rate of 1.60%.

As of June 30, 2020, unrecognized compensation cost related to outstanding non-vested stock awards was $74. The weighted average period over which the expense is expected to be recognized is 2.9 years. The aggregate market value of the shares released on the vesting dates was $22 for the six months ended June 30, 2020.