Stockholders' Equity - Reconciliation of total stockholders' equity (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
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, 2013	$ 1,245,286
Issuance of common stock	373
Common stock redemptions	(227)
Stock-based compensation	1,516
Net income	3,963	(1,018)
Dividends to common stockholders ($0.90 per share)	(28,802)
Distributions to non-controlling interests	(315)
Balance at March 31, 2014	1,221,794
Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2013	959
Issuance of common stock
Common stock redemptions
Stock-based compensation	1
Net income
Dividends to common stockholders ($0.90 per share)
Distributions to non-controlling interests
Balance at March 31, 2014	960
Additional Paid-In Capital [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2013	2,325,228
Issuance of common stock	373
Common stock redemptions	(227)
Stock-based compensation	1,515
Net income
Dividends to common stockholders ($0.90 per share)
Distributions to non-controlling interests
Balance at March 31, 2014	2,326,889
Accumulated Other Comprehensive Loss [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2013	51
Issuance of common stock
Common stock redemptions
Stock-based compensation
Net income
Dividends to common stockholders ($0.90 per share)
Distributions to non-controlling interests
Balance at March 31, 2014	51
Cumulative Net Income Attributable to Common Stockholders [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2013	808,362
Issuance of common stock
Common stock redemptions
Stock-based compensation
Net income	3,852
Dividends to common stockholders ($0.90 per share)
Distributions to non-controlling interests
Balance at March 31, 2014	812,214
Cumulative Dividends [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2013	(1,891,123)
Issuance of common stock
Common stock redemptions
Stock-based compensation
Net income
Dividends to common stockholders ($0.90 per share)	(28,802)
Distributions to non-controlling interests
Balance at March 31, 2014	(1,919,925)
Total Stockholders' Equity [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2013	1,243,477
Issuance of common stock	373
Common stock redemptions	(227)
Stock-based compensation	1,516
Net income	3,852
Dividends to common stockholders ($0.90 per share)	(28,802)
Distributions to non-controlling interests
Balance at March 31, 2014	1,220,189
Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2013	1,809
Issuance of common stock
Common stock redemptions
Stock-based compensation
Net income	111
Dividends to common stockholders ($0.90 per share)
Distributions to non-controlling interests	(315)
Balance at March 31, 2014	$ 1,605