CONSOLIDATED STATEMENTS OF EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Additional Paid-In Capital	Distributions in Excess of Accumulated Earnings	Accumulated Other Comprehensive Income (Loss)	Non-controlling Interest
Balance at Dec. 31, 2011	$ 1,409,644	$ 483	$ 1,545,563	$ (392,378)	$ 0	$ 255,976
Balance (in shares) at Dec. 31, 2011		48,321,305
Increase (Decrease) in Stockholders' Equity
Net income	163,622			135,302		28,320
Unrealized gain (loss) on interest rate swap agreements	(1,296)				(1,069)	(227)
Issuance of common stock, net	165,968	30	165,938
Issuance of common stock, net (in shares)		2,966,742
Stock-based compensation	13,923		13,923
Stock-based compensation (in shares)		4,199
Repurchase of common stock	(4,245)	(1)	(4,244)
Repurchase of common stock (in shares)		(68,284)
Conversion of UPREIT Units for common stock	0	3	6,896			(6,899)
Conversion of UPREIT Units for common stock (in shares)		284,180
Adjustment of noncontrolling interest	0		(18,157)			18,157
Dividends and distributions paid	(159,349)			(131,321)		(28,028)
Balance at Dec. 31, 2012	1,588,267	515	1,709,919	(388,397)	(1,069)	267,299
Balance (in shares) at Dec. 31, 2012	51,508,142	51,508,142
Increase (Decrease) in Stockholders' Equity
Net income	124,349			103,954		20,395
Unrealized gain (loss) on interest rate swap agreements	1,770				1,464	306
Issuance of common stock, net	46,593	9	46,584
Issuance of common stock, net (in shares)		886,400
Issuance of common stock through public offering, net	267,633	44	267,589
Issuance of common stock through public offering, net (in shares)		4,427,500
Stock-based compensation	7,788		7,788
Stock-based compensation (in shares)		3,137
Repurchase of common stock	(3,075)		(3,075)
Repurchase of common stock (in shares)		(47,460)
Conversion of UPREIT Units for common stock	0	1	2,865			(2,866)
Conversion of UPREIT Units for common stock (in shares)		110,537
Adjustment of noncontrolling interest	0		(27,870)			27,870
Dividends and distributions paid	(134,565)			(112,736)		(21,829)
Balance at Sep. 30, 2013	$ 1,898,760	$ 569	$ 2,003,800	$ (397,179)	$ 395	$ 291,175
Balance (in shares) at Sep. 30, 2013	56,888,256	56,888,256