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Share-Based Compensation (Tables)
 12 Months Ended
Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]  
Summary of Total Compensation Cost Recognized for Share-Based Awards

Total compensation cost recognized for share-based awards was as follows for the years ended December 31, 2020, 2019, and 2018 (in thousands):

 

 

2020

 

 

2019

 

 

2018

 

Share-based compensation expense (1)

 

$

8,295

 

 

$

8,146

 

 

$

8,550

 

Capitalized share-based compensation (2)

 

 

946

 

 

 

962

 

 

 

1,215

 

   Total share-based compensation (3)

 

$

9,241

 

 

$

9,108

 

 

$

9,765

 

 

(1)

Amounts are recorded in general and administrative expenses on the consolidated statements of operations.

(2)

Amounts are recorded in building and improvements on the consolidated balance sheets.

(3)

Amounts are recorded in additional paid-in capital and common noncontrolling interests in the AIR Operating Partnership on the AIR consolidated balance sheets, and in general partner and special limited partner and limited partners on the AIR Operating Partnership consolidated balance sheets.
Assumptions Used in Determination of Grant-Date Fair Value of Awards The valuation assumptions for the 2020, 2019, and 2018 grants were as follows:

 

 

2020

 

 

2019

 

 

2018

 

Grant date market value of a common share

 

$

53.26

 

 

$

49.24

 

 

$

40.95

 

Risk-free interest rate

 

1.48% - 1.58%

 

 

2.59% - 2.66%

 

 

2.32% - 2.68%

 

Dividend yield

 

 

2.93

%

 

 

3.09

%

 

 

3.52

%

Expected volatility

 

15.82% - 16.84%

 

 

19.08% - 19.24%

 

 

17.64% - 18.02%

 

Derived vesting period of TSR Restricted Stock and TSR LTIP I units

 

3.5 years

 

 

3.4 years

 

 

3.4 years

 

Weighted average expected term of TSR Stock Options and LTIP II units

 

5.9 years

 

 

5.8 years

 

 

5.6 years