Stockholders' Equity - Reconciliation of total stockholders' equity (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Dividends per share declared to common stockholders (in dollars per share)	$ 0.30	$ 0.30	$ 0.90	$ 0.90
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2012			$ 1,120,944
Issuance of common stock			220,043
Common stock redemptions			(247)
Stock-based compensation			4,131
Total comprehensive loss	19,783	5,835	(5,473)	11,897
Dividends to common stockholders ($0.90 per share)			(82,815)
Distributions to non-controlling interests			(3)
Proceeds from non-controlling interests			1,749
Balance at September 30, 2013	1,258,329		1,258,329
Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2012			875
Issuance of common stock			83
Common stock redemptions			0
Stock-based compensation			1
Total comprehensive loss			0
Dividends to common stockholders ($0.90 per share)			0
Distributions to non-controlling interests			0
Proceeds from non-controlling interests			0
Balance at September 30, 2013	959		959
Additional Paid-In Capital [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2012			2,100,297
Issuance of common stock			219,960
Common stock redemptions			(247)
Stock-based compensation			4,130
Total comprehensive loss			0
Dividends to common stockholders ($0.90 per share)			0
Balance at September 30, 2013	2,324,140		2,324,140
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 ($0.90 per share)			0
Distributions to non-controlling interests			0
Proceeds from non-controlling interests			0
Balance at September 30, 2013	(2,092)		(2,092)
Cumulative Net Income Attributable to Common Stockholders [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			(5,439)
Dividends to common stockholders ($0.90 per share)			0
Distributions to non-controlling interests			0
Proceeds from non-controlling interests			0
Balance at September 30, 2013	795,977		795,977
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 ($0.90 per share)			(82,815)
Distributions to non-controlling interests			0
Proceeds from non-controlling interests			0
Balance at September 30, 2013	(1,862,367)		(1,862,367)
Total Stockholders' Equity [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2012			1,120,944
Issuance of common stock			220,043
Common stock redemptions			(247)
Stock-based compensation			4,131
Total comprehensive loss			(5,439)
Dividends to common stockholders ($0.90 per share)			(82,815)
Distributions to non-controlling interests			0
Proceeds from non-controlling interests			0
Balance at September 30, 2013	1,256,617		1,256,617
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			(34)
Dividends to common stockholders ($0.90 per share)			0
Distributions to non-controlling interests			(3)
Proceeds from non-controlling interests			1,749
Balance at September 30, 2013	$ 1,712		$ 1,712