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Stock Based Compensation | 12 Months Ended
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Dec. 31, 2016
Stock Based Compensation [Abstract] |
Disclosure of Compensation Related Costs, Share-based Payments [Text Block] | 5. STOCK BASED COMPENSATION Overview MAA accounts for its stock based employee compensation plans in accordance with accounting standards governing stock based compensation. These standards require an entity to measure the cost of employee services received in exchange for an award of an equity instrument based on the award's fair value on the grant date and recognize the cost over the period during which the employee is required to provide service in exchange for the award, which is generally the vesting period. Any liability awards issued are remeasured at each reporting period. MAA’s stock compensation plans consist of an employee stock purchase plan and a number of incentives provided to attract and retain independent directors, executive officers and key employees. Incentives are currently granted under the 2013 Stock Incentive Plan, as amended, which was originally approved at the September 27, 2013 annual meeting of MAA shareholders. The 2013 Stock Incentive Plan replaced the 2004 Stock Plan (collectively, the “Plans”) under which no further awards may be granted as of October 31, 2013. The 2004 Stock Plan allowed for the grant of restricted stock and stock options up to a total of 500,000 shares. The 2013 Stock Incentive Plan allows for the grant of restricted stock and stock options up to 625,000 shares. MAA believes that such awards better align the interests of its employees with those of its shareholders. Compensation expense is generally recognized for service based restricted stock awards using the straight-line method over the vesting period of the shares regardless of cliff or ratable vesting distinctions. Compensation expense for market and performance based restricted stock awards is generally recognized using the accelerated amortization method with each vesting tranche valued as a separate award, with a separate vesting date, consistent with the estimated value of the award at each period end. Additionally, we adjust compensation expense for estimated and actual forfeitures for all awards. Compensation expense for stock options is generally recognized on a straight-line basis over the requisite service period. MAA presents stock compensation expense in the Consolidated Statements of Operations on the line labeled “General and administrative expenses”. Total compensation costs under the Plans were approximately $12.2 million, $6.9 million and $5.2 million for the years ended December 31, 2016, 2015, and 2014, respectively. Of these amounts, total compensation costs capitalized under the Plans were approximately $697,000, $735,000, and $431,000 for the years ended December 31, 2016, 2015, and 2014, respectively. As of December 31, 2016, the total unrecognized compensation cost related to the Plans was approximately $8.1 million. This cost is expected to be recognized over the remaining weighted average period of 1.1 years. Total cash paid for the settlement of plan shares totaled $2.0 million, $1.0 million, and $0.6 million for the years ended December 31, 2016, 2015, and 2014, respectively. Information concerning grants under the Plans is listed below. Restricted Stock In general, restricted stock is earned based on either a service condition, performance condition, or market condition, or a combination thereof, and vests ratably over a period from 1 year to 5 years. Service based awards are earned when the employee remains employed over the requisite service period and are valued on the grant date based upon the market price of MAA common stock on the date of grant. Market based awards are earned when MAA reaches a specified stock price or specified return on the stock price (price appreciation plus dividends) and are valued on the grant date using a Monte Carlo simulation. Performance based awards are earned when MAA reaches certain operational goals such as FFO targets and are valued based upon the market price of MAA common stock on the date of grant as well as the probability of reaching the stated targets. MAA remeasures the fair value of the performance based awards each balance sheet date with adjustments made on a cumulative basis until the award is settled and the final compensation is known. The weighted average grant date fair value per share of restricted stock awards granted during the years ended December 31, 2016, 2015, and 2014, was $73.20, $68.35, and $62.40, respectively. The following is a summary of the key assumptions used in the valuation calculations for market based awards granted during the years ended December 31, 2016, 2015, and 2014:
| 2016 | 2015 | 2014
Risk free rate - minimum | 0.49% | 0.10% | 0.02%
Risk free rate - maximum | 1.27% | 1.05% | 0.80%
Dividend yield | 3.634% | 3.932% | 4.755%
Volatility - minimum | 18.41% | 15.41% | 18.31%
Volatility - maximum | 19.45% | 16.04% | 20.48%
Service period | 3 years | 3 years | 3 years
The risk free rate was based on a zero coupon risk-free rate. The minimum risk free rate was based on a period of 0.25 years for the years ended December 31, 2016, 2015, and 2014. The maximum risk free rate was based on a period of 3 years for the years ended December 31, 2016, 2015, and 2014. The dividend yield was based on the closing stock price of MAA stock on the date of grant. Volatility for MAA was obtained by using a blend of both historical and implied volatility calculations. Historical volatility was based on the standard deviation of daily total continuous returns, and implied volatility was based on the trailing month average of daily implied volatilities interpolating between the volatilities implied by stock call option contracts that were closest to the terms shown and closest to the money. The minimum volatility was based on a period of 2 years, 1 year, and 1 year for the years ended December 31, 2016, 2015, and 2014, respectively. The maximum volatility was based on a period of 1 year, 2 years, and 3 years for the years ended December 31, 2016, 2015, and 2014, respectively. The requisite service period is based on the criteria for the separate programs according to the vesting schedule. Turnover is based on the historical experience for the key managers and executive officers, and is used in estimating forfeitures. A summary of the status of the nonvested restricted shares as of December 31, 2016, and the changes for the year ended December 31, 2016, is presented below:
Nonvested Shares |  | Shares |  | Weighted Average Grant-Date Fair Value
Nonvested at January 1, 2016 |  | 187,941 |  |  | $ | 63.36 |
Issued |  | 119,039 |  |  | 79.51 |
Vested |  | (80,342 | ) |  | 64.00 |
Forfeited |  | (1,014 | ) |  | 71.84 |
Nonvested at December 31, 2016 |  | 225,624 |  |  | $ | 71.61 |
The total fair value of shares vested during the years ended December 31, 2016, 2015, and 2014 was approximately $5.1 million, $2.9 million, and $2.7 million, respectively. Stock Options In general, stock options are earned when the employee remains employed over the requisite service period and vest ratably over a period from 0.3 years to 2.3 years. Stock options exercised result in new common shares being issued on the open market by the Company. The fair value of stock option awards is determined using the Black-Scholes or Monte Carlo valuation models. The weighted average grant date fair value of stock option awards granted during the year ended December 31, 2016 was $18.08 per option. All options issued during the year ended December 31, 2016 related to options exchanged during the Post Merger. All options were fully vested at merger. No stock options were granted during the years ended December 31, 2015 and 2014. The following is a summary of the key assumptions used in the Monte Carlo valuation calculations for stock options granted during the year ended December 31, 2016:
|  | 2016
Term - minimum |  | 1.11 years
Term - maximum |  | 2.11 years
Risk free rate - minimum |  | 0.64%
Risk free rate - maximum |  | 2.63%
Dividend yield |  | 3.81%
Volatility - minimum |  | 21.02%
Volatility - maximum |  | 21.57%
The term represents an estimate of the period of time options are expected to remain outstanding. The U.S. Treasury bill rate, which approximated the expected life of the option, was used to represent the risk-free rate. The current dividend yield at the time of grant was used to estimate the dividend yield over the life of the option. Volatility is based on the actual changes in the market value of MAA’s stock and is calculated using daily market value changes from the date of grant over a past period equal to the expected life of the stock options. Turnover is based on the historical rate at which options are exercised, and is used in estimating forfeitures. A summary of the status of the stock options as of December 31, 2016 and the changes for the year ended December 31, 2016 is presented below:
Stock Options |  | Options |  | Weighted Average Exercise Price
Outstanding at January 1, 2016 |  | 58,112 |  |  | $ | 86.21 |
Granted |  | 108,198 |  |  | 75.58 |
Exercised |  | — |  |  | — |
Expired |  | (19,028 | ) |  | 103.56 |
Outstanding at December 31, 2016 |  | 147,282 |  |  | $ | 76.16 |
All 147,282 options outstanding at December 31, 2016 were exercisable with a weighted average exercise price of $76.16, an intrinsic value of $3,400,000, and a weighted average remaining term of 6.1 years. No options were exercised during the year ended December 31, 2016. There was no cash received from the exercise of stock options for the year ended December 31, 2016. Cash received from the exercise of stock options for the years ended December 31, 2015 and 2014 was $0.4 million and $12.2 million, respectively.

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- Definition The entire disclosure for compensation-related costs for equity-based compensation, which may include disclosure of policies, compensation plan details, allocation of equity compensation, incentive distributions, equity-based arrangements to obtain goods and services, deferred compensation arrangements, employee stock ownership plan details and employee stock purchase plan details. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 40 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=65895303&loc=d3e17540-113929 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 50 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=68057994&loc=d3e25284-112666 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5444-113901 + Details
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