Stockholders' Equity (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Dividends per share declared to common stockholders (in dollars per share)	$ 0.30	$ 0.30
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2012	$ 1,120,944
Issuance of common stock	40,374
Common stock redemptions	(156)
Stock-based compensation	1,848
Total comprehensive loss	(1,018)	3,134
Dividends to common stockholders ($0.30 per share)	(26,746)
Distributions to non-controlling interests	(3)
Proceeds from non-controlling interests	1,373
Ending Balance	1,136,616
Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2012	875
Issuance of common stock	16
Common stock redemptions	0
Stock-based compensation	1
Total comprehensive loss	0
Dividends to common stockholders ($0.30 per share)	0
Distributions to non-controlling interests	0
Proceeds from non-controlling interests	0
Ending Balance	892
Additional Paid-In Capital [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2012	2,100,297
Issuance of common stock	40,358
Common stock redemptions	(156)
Stock-based compensation	1,847
Total comprehensive loss	0
Dividends to common stockholders ($0.30 per share)	0
Ending Balance	2,142,346
Accumulated Other Comprehensive Loss [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2012	(2,092)
Issuance of common stock	0
Common stock redemptions	0
Stock-based compensation	0
Total comprehensive loss	0
Dividends to common stockholders ($0.30 per share)	0
Distributions to non-controlling interests	0
Proceeds from non-controlling interests	0
Ending Balance	(2,092)
Cumulative Net Income [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2012	801,416
Issuance of common stock	0
Common stock redemptions	0
Stock-based compensation	0
Total comprehensive loss	(999)
Dividends to common stockholders ($0.30 per share)	0
Distributions to non-controlling interests	0
Proceeds from non-controlling interests	0
Ending Balance	800,417
Cumulative Dividends [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2012	(1,779,552)
Issuance of common stock	0
Common stock redemptions	0
Stock-based compensation	0
Total comprehensive loss	0
Dividends to common stockholders ($0.30 per share)	(26,746)
Distributions to non-controlling interests	0
Proceeds from non-controlling interests	0
Ending Balance	(1,806,298)
Total Stockholders' Equity [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2012	1,120,944
Issuance of common stock	40,374
Common stock redemptions	(156)
Stock-based compensation	1,848
Total comprehensive loss	(999)
Dividends to common stockholders ($0.30 per share)	(26,746)
Distributions to non-controlling interests	0
Proceeds from non-controlling interests	0
Ending Balance	1,135,265
Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2012	0
Issuance of common stock	0
Common stock redemptions	0
Stock-based compensation	0
Total comprehensive loss	(19)
Dividends to common stockholders ($0.30 per share)	0
Distributions to non-controlling interests	(3)
Proceeds from non-controlling interests	1,373
Ending Balance	$ 1,351