Noncontrolling Interests (Redeemable Preferred Units) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning Balance	$ 55,652
Net income	3,497	3,339	3,343
Payments for redemption of preferred units	(18,329)	0	0
Conversion of redeemable preferred units (Series Two Preferred Units) to common units	5,852
Ending Balance	110,876	55,652
Redeemable Preferred Units [Member]
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning Balance	55,652	55,652	55,652
Issuance of redeemable preferred units (Series Four Preferred Units	79,405
Net income	3,497	3,339	3,343
Distributions	(3,497)	(3,339)	(3,343)
Payments for redemption of preferred units	(18,329)
Conversion of redeemable preferred units (Series Two Preferred Units) to common units	(5,852)
Ending Balance	$ 110,876	$ 55,652	$ 55,652