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Share and Unit-Based Plans: Long-Term Incentive Plan Units (Details) |  |  |  |  |  |  |  |  |  |  | 12 Months Ended
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Jan. 07, 2016 | Dec. 31, 2015 shares | Jan. 12, 2015 | Jan. 01, 2015 $ / shares shares | Dec. 31, 2014 shares | Mar. 07, 2014 $ / shares shares | Jan. 16, 2014 | Jan. 01, 2014 $ / shares shares | Dec. 31, 2013 shares | Feb. 15, 2013 $ / shares shares | Dec. 31, 2015 $ / shares shares | Dec. 31, 2014 $ / shares shares | Dec. 31, 2013 $ / shares shares
Stock units |  |  |  |  |  |  |  |  |  |  |  |  |
Share and unit-based plans |  |  |  |  |  |  |  |  |  |  |  |  |
Conversion rate |  |  |  |  |  |  |  |  |  |  | 1 |  |
Granted (in shares) |  |  |  |  |  |  |  |  |  |  | 77,282 | 75,309 | 67,920
Granted (in dollars per share) | $ / shares |  |  |  |  |  |  |  |  |  |  | $ 86.53 | $ 60.50 | $ 62.01
Vested (in shares) |  |  |  |  |  |  |  |  |  |  | 86,761 | 68,253 | 45,279
Forfeited (in shares) |  |  |  |  |  |  |  |  |  |  | 2,809 | 0 | 0
LTIP units |  |  |  |  |  |  |  |  |  |  |  |  |
Share and unit-based plans |  |  |  |  |  |  |  |  |  |  |  |  |
Conversion rate |  |  |  |  |  |  |  |  |  |  | 1 |  |
Granted (in shares) |  |  |  |  |  |  |  |  |  |  | 424,442 | 725,908 | 332,189
Granted (in dollars per share) | $ / shares |  |  |  |  |  |  |  |  |  |  | $ 74.71 | $ 51.71 | $ 66.58
Absolute return requirement (in shares) |  |  |  | 3.00% |  |  |  |  |  |  |  |  |
Level of percentile ranking at which awards vested (as a percent) |  |  | 150.00% |  |  |  | 96.00% |  |  |  |  |  |
Vested (in shares) |  |  |  |  |  |  |  |  | 318,900 |  | 414,822 | 679,213 | 518,900
Forfeited (in shares) |  |  |  |  |  |  |  |  | 13,289 |  | 0 | 0 | 13,289
Risk free rate (as a percent) |  |  |  | 0.25% |  |  |  |  |  |  |  |  |
Volatility rate (as a percent) |  |  |  | 16.81% |  |  |  |  |  |  |  |  |
Long Term Incentive Plan, Market Indexed |  |  |  |  |  |  |  |  |  |  |  |  |
Share and unit-based plans |  |  |  |  |  |  |  |  |  |  |  |  |
Vested (in shares) |  | 55,934 |  |  | 136,465 |  |  |  |  |  |  |  |
Executive Officer | LTIP units |  |  |  |  |  |  |  |  |  |  |  |  |
Share and unit-based plans |  |  |  |  |  |  |  |  |  |  |  |  |
Granted (in shares) |  |  |  |  |  |  |  |  |  | 332,189 |  |  |
Granted (in dollars per share) | $ / shares |  |  |  |  |  | $ 60.25 |  |  |  | $ 66.58 |  |  |
Executive Officer | LTIP units | 2014 LTIP Units Series 2 |  |  |  |  |  |  |  |  |  |  |  |  |
Share and unit-based plans |  |  |  |  |  |  |  |  |  |  |  |  |
Granted (in shares) |  |  |  |  |  |  |  | 70,042 |  |  |  |  |
Granted (in dollars per share) | $ / shares |  |  |  |  |  |  |  | $ 58.89 |  |  |  |  |
Executive Officer | LTIP units | 2014 LTIP Units Series 1 |  |  |  |  |  |  |  |  |  |  |  |  |
Share and unit-based plans |  |  |  |  |  |  |  |  |  |  |  |  |
Granted (in shares) |  |  |  |  |  | 246,471 |  | 272,930 |  |  |  |  |
Granted (in dollars per share) | $ / shares |  |  |  |  |  |  |  | $ 45.34 |  |  |  |  |
Executive Officer | LTIP units | 2015 LTIP Units Series 1 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Share and unit-based plans |  |  |  |  |  |  |  |  |  |  |  |  |
Granted (in shares) |  |  |  | 49,451 |  |  |  |  |  |  |  |  |
Granted (in dollars per share) | $ / shares |  |  |  | $ 83.41 |  |  |  |  |  |  |  |  |
Executive Officer | LTIP units | 2015 LTIP Units Series 2 |  |  |  |  |  |  |  |  |  |  |  |  |
Share and unit-based plans |  |  |  |  |  |  |  |  |  |  |  |  |
Granted (in shares) |  |  |  | 186,450 |  |  |  |  |  |  |  |  |
Granted (in dollars per share) | $ / shares |  |  |  | $ 66.37 |  |  |  |  |  |  |  |  |
Subsequent Event | LTIP units |  |  |  |  |  |  |  |  |  |  |  |  |
Share and unit-based plans |  |  |  |  |  |  |  |  |  |  |  |  |
Level of percentile ranking at which awards vested (as a percent) | 130.00% |  |  |  |  |  |  |  |  |  |  |  |

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- Definition Represents the level of percentile ranking terms of total return per common stock share to the total return of a group of peer REITs at which the equity instruments other than options vested during the period. + References No definition available. + Details
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- Definition Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments, Other than Options, Conversion Rate + References No definition available. + Details
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- Definition Share-based Compensation Arrangement by Share-based Payment Award Equity Instruments other than Options, Absolute Return Requirement + References No definition available. + Details
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- Definition The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(iv)(3) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The risk-free interest rate assumption that is used in valuing an option on its own shares. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(iv) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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