Unsecured Exchangeable Senior Notes Unsecured Exchangeable Senior Notes (Narrative) (details) (USD $)	3 Months Ended		6 Months Ended			0 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	May 18, 2013 3.75% xchangeable Senior Notes [Member]	May 18, 2013 3.75% xchangeable Senior Notes [Member] Redeemed amount [Member]	May 18, 2013 3.75% xchangeable Senior Notes [Member] Submitted for Exchange [Member]
Debt Instrument [Line Items]
Coupon/Stated Rate						3.75%
Redemption Date						May 18, 2013
Debt Instrument Redemption Price Principal Percentage						100.00%
Repayments of Unsecured Debt							$ 990,000	$ 449,010,000
Shares issued as part of the exchange	152,463,640		152,463,640		151,680,119	419,116
Losses from early extinguishment of debt	$ (152,000)	$ (274,000)	$ (152,000)	$ (1,041,000)		$ 100,000