(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