Stockholders' Equity - Reconciliation of total stockholders' equity (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Increase (Decrease) in Stockholders' Equity [Rollforward]
Net income	$ 33,134	$ 50,778
Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2015	1,015
Issuance of common stock	142
Common stock redemptions	0
Stock-based compensation	3
Net income	0
Reclassification of loss on forward starting interest rate swaps	0
Dividends to common stockholders ($0.90 per share)	0
Balance at September 30, 2016	1,160
Additional Paid-In Capital [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2015	2,461,376
Issuance of common stock	450,204
Common stock redemptions	(410)
Stock-based compensation	5,646
Net income	0
Reclassification of loss on forward starting interest rate swaps	0
Dividends to common stockholders ($0.90 per share)	0
Balance at September 30, 2016	2,916,816
Accumulated Other Comprehensive Loss [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2015	(1,569)
Issuance of common stock	0
Common stock redemptions	0
Stock-based compensation	0
Net income	0
Reclassification of loss on forward starting interest rate swaps	126
Dividends to common stockholders ($0.90 per share)	0
Balance at September 30, 2016	(1,443)
Cumulative Net Income Attributable to Common Stockholders [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2015	909,685
Issuance of common stock	0
Common stock redemptions	0
Stock-based compensation	0
Net income	33,134
Reclassification of loss on forward starting interest rate swaps	0
Dividends to common stockholders ($0.90 per share)	0
Balance at September 30, 2016	942,819
Cumulative Dividends [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2015	(2,127,760)
Issuance of common stock	0
Common stock redemptions	0
Stock-based compensation	0
Net income	0
Reclassification of loss on forward starting interest rate swaps	0
Dividends to common stockholders ($0.90 per share)	(96,998)
Balance at September 30, 2016	$ (2,224,758)
Dividends per share paid to common stockholders (in dollars per share)	$ 0.90
Total Stockholders' Equity [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2015	$ 1,242,747
Issuance of common stock	450,346
Common stock redemptions	(410)
Stock-based compensation	5,649
Net income	33,134
Reclassification of loss on forward starting interest rate swaps	126
Dividends to common stockholders ($0.90 per share)	(96,998)
Balance at September 30, 2016	$ 1,634,594