2. Significant Accounting Policies Schedule of Redeemable Noncontrolling Interests - Operating Partnership (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Accounting Policies [Abstract]
Balance at December 31, 2012, units			18,786,806
Balance at December 31, 2012			$ 453,889
Net income attributable to redeemable noncontrolling interests – operating partnership	2,965	2,006	4,938	3,576
Distributions declared			(7,161)
Redemption of operating partnership units, shares			(2,891,269)
Redemption of operating partnership units			(69,900)	(5,700)
Adjustments to redeemable noncontrolling interests – operating partnership			2,111	83,333
Balance at March 31, 2013, units	15,895,537		15,895,537
Balance at March 31, 2013	$ 383,877		$ 383,877