Share-Based Compensation	9 Months Ended
Sep. 30, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation	Share-Based Compensation During the first nine months of 2013, we granted share-based compensation to eligible participants under our Long-Term Incentive Plan. We recognize expense on all share-based grants over the service period, which is the shorter of the period until the employees’ retirement eligibility dates and the service period of the award for awards expected to vest. Expense is generally reduced for estimated forfeitures. MARKET SHARE UNITS We granted 361,308 market share units, or MSUs, during the first nine months of 2013. Generally, half of the MSUs vest after a two-year period and the other half after a three-year period, in each case, based on our actual stock price performance during such periods. The number of MSUs earned will vary from zero to 150% of the number of MSUs awarded depending on the actual performance of our stock price. In the case of termination of employment due to death, disability or retirement during the performance period, vesting will be pro-rated based on the number of full months employed in 2013. Awards earned will be issued at the end of the two-year and three-year periods. MSUs may vest earlier in the case of a change in control. Each MSU earned will be settled in common stock. We estimated the fair value of each MSU granted on the date of grant using a Monte Carlo simulation that used the assumptions noted below. The MSUs granted during the first nine months of 2013 had a weighted average fair value of $34.55. Volatility was based on stock price history immediately prior to grant for a period commensurate with the remaining life of the plan. The risk-free rate was based on zero coupon U.S. government issues at the time of grant. The expected term represents the period from the valuation date to the end of the performance period. The weighted-average assumptions used in the valuations were as follows: expected volatility of 60.97%, risk-free rate of 0.35%, expected term (in years) of 2.38 and expected dividends of zero. RESTRICTED STOCK UNITS We granted restricted stock units, or RSUs, with respect to 24,500 shares of common stock during the first nine months of 2013 that vest four years from the date of grant. RSUs granted as special retention awards generally vest after a specified number of years from the date of grant or at a specified date, and RSUs granted with performance goals vest if those goals are attained. Generally, RSUs may vest earlier in the case of death, disability, retirement or a change in control. Each RSU is settled in a share of our common stock after the vesting period. The fair value of each RSU granted is equal to the closing price of our common stock on the date of grant. The RSUs granted during the first nine months of 2013 had a weighted average fair value of $29.89. PERFORMANCE SHARES We granted 104,543 performance shares during the first nine months of 2013. The performance shares generally vest after a three-year period based on our total stockholder return relative to the performance of the Dow Jones U.S. Construction and Materials Index, with adjustments to that index in certain circumstances, for the three-year period. The number of performance shares earned will vary from zero to 200% of the number of performance shares awarded depending on that relative performance. Vesting will be pro-rated based on the number of full months employed during the performance period in the case of death, disability, retirement or a change-in-control, and pro-rated awards earned will be issued at the end of the three-year period. Each performance share earned will be settled in common stock. We estimated the fair value of each performance share granted on the date of grant using a Monte Carlo simulation that used the assumptions noted below. The performance shares granted during the first nine months of 2013 had a weighted average fair value of $38.89. Expected volatility was based on implied volatility of our traded options and the daily historical volatilities of our peer group. The risk-free rate was based on zero coupon U.S. government issues at the time of grant. The expected term represents the period from the valuation date to the end of the performance period. The weighted average assumptions used in the valuations were as follows: expected volatility of 59.98%, risk-free rate of 0.43%, expected term (in years) of 2.88 and expected dividends of zero.

Share-Based Compensation

During the first nine months of 2013, we granted share-based compensation to eligible participants under our Long-Term Incentive Plan. We recognize expense on all share-based grants over the service period, which is the shorter of the period until the employees’ retirement eligibility dates and the service period of the award for awards expected to vest. Expense is generally reduced for estimated forfeitures.

MARKET SHARE UNITS

We granted 361,308 market share units, or MSUs, during the first nine months of 2013. Generally, half of the MSUs vest after a two-year period and the other half after a three-year period, in each case, based on our actual stock price performance during such periods. The number of MSUs earned will vary from zero to 150% of the number of MSUs awarded depending on the actual performance of our stock price. In the case of termination of employment due to death, disability or retirement during the performance period, vesting will be pro-rated based on the number of full months employed in 2013. Awards earned will be issued at the end of the two-year and three-year periods. MSUs may vest earlier in the case of a change in control. Each MSU earned will be settled in common stock.

We estimated the fair value of each MSU granted on the date of grant using a Monte Carlo simulation that used the assumptions noted below. The MSUs granted during the first nine months of 2013 had a weighted average fair value of $34.55. Volatility was based on stock price history immediately prior to grant for a period commensurate with the remaining life of the plan. The risk-free rate was based on zero coupon U.S. government issues at the time of grant. The expected term represents the period from the valuation date to the end of the performance period.

The weighted-average assumptions used in the valuations were as follows: expected volatility of 60.97%, risk-free rate of 0.35%, expected term (in years) of 2.38 and expected dividends of zero.

RESTRICTED STOCK UNITS

We granted restricted stock units, or RSUs, with respect to 24,500 shares of common stock during the first nine months of 2013 that vest four years from the date of grant. RSUs granted as special retention awards generally vest after a specified number of years from the date of grant or at a specified date, and RSUs granted with performance goals vest if those goals are attained. Generally, RSUs may vest earlier in the case of death, disability, retirement or a change in control. Each RSU is settled in a share of our common stock after the vesting period. The fair value of each RSU granted is equal to the closing price of our common stock on the date of grant. The RSUs granted during the first nine months of 2013 had a weighted average fair value of $29.89.

PERFORMANCE SHARES

We granted 104,543 performance shares during the first nine months of 2013. The performance shares generally vest after a three-year period based on our total stockholder return relative to the performance of the Dow Jones U.S. Construction and Materials Index, with adjustments to that index in certain circumstances, for the three-year period. The number of performance shares earned will vary from zero to 200% of the number of performance shares awarded depending on that relative performance. Vesting will be pro-rated based on the number of full months employed during the performance period in the case of death, disability, retirement or a change-in-control, and pro-rated awards earned will be issued at the end of the three-year period. Each performance share earned will be settled in common stock.

We estimated the fair value of each performance share granted on the date of grant using a Monte Carlo simulation that used the assumptions noted below. The performance shares granted during the first nine months of 2013 had a weighted average fair value of $38.89. Expected volatility was based on implied volatility of our traded options and the daily historical volatilities of our peer group. The risk-free rate was based on zero coupon U.S. government issues at the time of grant. The expected term represents the period from the valuation date to the end of the performance period.

The weighted average assumptions used in the valuations were as follows: expected volatility of 59.98%, risk-free rate of 0.43%, expected term (in years) of 2.88 and expected dividends of zero.