Earnings per Share and Unit (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended
	Jul. 15, 2016	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Income per common unit - diluted
Weighted Average Limited Partnership Units Outstanding, Basic		154,170,000		154,170
Parent Company [Member]
Earnings Per Share [Abstract]
Income from operations		$ 40,096	$ 32,623	$ 80,804	$ 62,811
Gain on sale of real estate				13,417	6,460
Net income attributable to common stockholders		$ 34,810	$ 32,480	$ 82,687	$ 57,653
Weighted average common units outstanding for basic EPU (in shares)		97,657,000	94,136,000	97,588,000	94,036,000
Weighted average common units outstanding for diluted EPU (in shares)		98,218,000	94,503,000	98,075,000	94,392,000
Income per common share/unit - basic:
Continuing operations (in dollars per share)		$ 0.36	$ 0.35	$ 0.85	$ 0.61
Income per common share/unit - diluted:
Continuing operations (in dollars per share)		$ 0.35	$ 0.34	$ 0.84	$ 0.61
Partnership Interest [Member]
Earnings Per Share [Abstract]
Income from operations		$ 40,096	$ 32,623	$ 80,804	$ 62,811
Gain on sale of real estate				$ 13,417	$ 6,460
Weighted average common units outstanding for basic EPU (in shares)		97,811,000	94,290,000	97,742,000	94,190,000
Weighted average common units outstanding for diluted EPU (in shares)		98,372,000	94,658,000	98,229,000	94,546,000
Income per common unit - basic
Continuing operations (in dollars per share)		$ 0.36	$ 0.35	$ 0.85	$ 0.61
Income per common unit - diluted
Continuing operations (in dollars per share)		$ 0.35	$ 0.34	$ 0.84	$ 0.61
Continuing Operations [Member] | Parent Company [Member]
Earnings Per Share [Abstract]
Net income attributable to common stockholders		$ 34,810	$ 32,480	$ 82,687	$ 57,653
Net income for common stock unit/holders - diluted		34,810	32,480	82,687	57,653
Continuing Operations [Member] | Partnership Interest [Member]
Earnings Per Share [Abstract]
Net income attributable to common stockholders		34,874	32,541	82,837	57,763
Net income for common stock unit/holders - diluted		$ 34,874	$ 32,541	$ 82,837	$ 57,763
Equity Offering [Member] | Subsequent Event [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Stock Issued During Period, Shares, New Issues	5,000,000