2. Significant Accounting Policies Schedule of Redeemable Noncontrolling Interests - Operating Partnership (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 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	1,973	1,570
Distributions declared	(3,187)
Redemption of operating partnership units, shares	(2,850,000)
Redemption of operating partnership units	(68,900)	(2,400)
Adjustments to redeemable noncontrolling interests – operating partnership	3,011	5,107
Balance at March 31, 2013, units	15,936,806
Balance at March 31, 2013	$ 386,786