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(Common Units) (Narrative) (Details) $ / shares in Units, $ in Millions |  |  |  |  |  | 12 Months Ended |
--- | --- | --- | --- | --- | --- | --- | ---
Oct. 30, 2015 $ / shares | Jul. 31, 2015 $ / shares | Apr. 30, 2015 $ / shares | Feb. 06, 2015 USD ($) shares | Jan. 28, 2015 $ / shares | Dec. 31, 2015 USD ($) yr $ / shares shares | Dec. 31, 2014 USD ($) shares | Dec. 17, 2015 $ / shares
OP Units [Member] |  |  |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |  |  |
Distributions Declared To OP And LTIP Units Per Unit |  |  |  |  |  |  |  | $ 0.65
Distributions Declared To OPP and MYLTIP Units Per Unit |  |  |  |  |  |  |  | 0.065
OP Units for redemption (in shares) | shares |  |  |  |  |  | 424,236 | 80,246 |
Redemption of OP units issued on conversion of Series Two Preferred Units (in shares) | shares |  |  |  |  |  | 0 | 3,734 |
Redemption of OP units issued on conversion of LTIP Units (in shares) | shares |  |  |  |  |  | 65,192 | 67,857 |
Outperformance Awards LTIP Units distribution as percentage of OP Unit distribution prior to measurement date |  |  |  |  |  | 10.00% |  |
Distributions made to OP and LTIP units per unit (in dollars per share) | $ 0.65 | $ 0.65 | $ 0.65 |  | $ 0.65 |  |  |
Distribution paid to outperformance awards, OPP Units and MYLTIP Units (in dollars per share) | $ 0.065 | $ 0.065 | 0.065 |  | 0.065 |  |  |
Restriction on redemption of OP Unit to Common Stock (in years) | yr |  |  |  |  |  | 1 |  |
Redemption of OP Unit equivalence to Common Stock (in shares) | shares |  |  |  |  |  | 1 |  |
Common units of operating partnership if converted value | $ |  |  |  |  |  | $ 2,300.0 |  |
Closing price of common stock (in dollars per share) |  |  |  |  |  | $ 127.54 |  |
OPP Units 2011 [Member] |  |  |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |  |  |
Accelerated Compensation Expenses Related To 2011 OPP Units | $ |  |  |  |  |  |  | $ 1.2 |
OPP Units 2012 [Member] |  |  |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |  |  |
Distributions made to OP and LTIP units per unit (in dollars per share) |  |  | $ 0.416 |  |  |  |  |
special dividend [Member] | OP Units [Member] |  |  |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |  |  |
Distributions Declared To OP And LTIP Units Per Unit |  |  |  |  |  |  |  | $ 1.25
Distributions made to OP and LTIP units per unit (in dollars per share) |  |  |  |  | $ 4.50 |  |  |
OPP Units 2012 [Member] |  |  |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |  |  |
Outperformance awards earned | $ |  |  |  | $ 32.1 |  |  |  |
Potential maximum amount of Outperformance Awards earned (percent) |  |  |  | 80.00% |  |  |  |
Potential Awards Earned | $ |  |  |  | $ 40.0 |  |  |  |
2012 OPP Units forfeited | shares |  |  |  | 174,549 |  |  |  |

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