Stockholders' Equity - Reconciliation of total stockholders' equity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Increase (Decrease) in Stockholders' Equity [Rollforward]
Net income	$ 9,156	$ 5,382
Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2015	1,015
Issuance of common stock	24
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 ($0.30 per share)	0
Balance at March 31, 2016	1,042
Additional Paid-In Capital [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2015	2,461,376
Issuance of common stock	70,202
Common stock redemptions	(393)
Stock-based compensation	1,945
Net income	0
Reclassification of loss on forward starting interest rate swaps	0
Dividends to common stockholders ($0.30 per share)	0
Balance at March 31, 2016	2,533,130
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	42
Dividends to common stockholders ($0.30 per share)	0
Balance at March 31, 2016	(1,527)
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	9,156
Reclassification of loss on forward starting interest rate swaps	0
Dividends to common stockholders ($0.30 per share)	0
Balance at March 31, 2016	918,841
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 ($0.30 per share)	(30,727)
Balance at March 31, 2016	$ (2,158,487)
Dividends per share paid to common stockholders (in dollars per share)	$ 0.30
Total Stockholders' Equity [Member]
Increase (Decrease) in Stockholders' Equity [Rollforward]
Balance at December 31, 2015	$ 1,242,747
Issuance of common stock	70,226
Common stock redemptions	(393)
Stock-based compensation	1,948
Net income	9,156
Reclassification of loss on forward starting interest rate swaps	42
Dividends to common stockholders ($0.30 per share)	(30,727)
Balance at March 31, 2016	$ 1,292,999