Stock Option and Incentive Plan (Restricted Stock) (Narrative) (Details) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) $ / shares shares	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) VestingInstallments $ / shares shares	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued | shares	153,552,831		153,552,831		153,192,845
Stock based Compensation Expense	$ 5,100	$ 6,200	$ 15,200	$ 16,000
Common Stock, Value, Issued	$ 1,535		$ 1,535		$ 1,531
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued | shares	34,150		34,150
Employee and director payment per share (in dollars per share) | $ / shares			$ 0.01
Common Stock, Value, Issued	$ 4,800		$ 4,800
Employee's weighted average cost per share (in dollars per share) | $ / shares	$ 140.88		$ 140.88
LTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
LTIP units issued (in shares) | shares	190,563		190,563
Value of LTIP units issued			$ 13,500
Per unit fair value weighted-average (in dollars per share) | $ / shares	$ 128.94		$ 128.94
Expected life assumed to calculate per unit fair value per LTIP unit (years)			5 years 8 months 12 days
Risk-free rate			1.47%
Expected price volatility			26.00%
2015 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
MYLTIP units issued (in shares) | shares	375,000		375,000
LTIPs And Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting annual installments | VestingInstallments			4
Unrecognized compensation expenses	$ 23,300		$ 23,300
LTIPs and 2015 MYLTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee and director payment per share (in dollars per share) | $ / shares			$ 0.25
Unvested 2012 OPP Units and 2013, 2014 and 2015 MYLTIPS [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expenses	$ 24,100		$ 24,100
Weighted-average period (years)	2 years 8 months 12 days
Non-executive Chairman of the Board of Directors [Member] | LTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
LTIP units issued (in shares) | shares	85,962		85,962