Quarterly Financial Information (Unaudited) (Summarized Unaudited Consolidated Quarterly Information) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 895,288	$ 899,928	$ 895,490	$ 883,443	$ 875,713	$ 867,116	$ 848,404	$ 852,289	$ 3,574,149	$ 3,443,522	$ 3,286,398
Income from continuing operations	178,835	156,930	152,272	155,912	142,575	150,446	137,849	123,339	643,949	554,209	389,539
Discontinued operations	(15)	(19)	(23)	(53)	(167)	(118)	(148)	(489)	(110)	(922)	11,103
Gain (loss) on real estate dispositions	214,985	458,280	719	43,289	66,424	(144)	5,739	26,184	717,273	98,203	18,580
Net income	393,805	615,191	152,968	199,148	208,832	150,184	143,440	149,034	1,361,112	651,490	419,222
Net income attributable to noncontrolling interests	1,251	1,233	1,137	1,021	1,195	732	278	54	4,642	2,259	1,379
Net income attributable to common stockholders	$ 392,554	$ 613,958	$ 151,831	$ 198,127	$ 207,637	$ 149,452	$ 143,162	$ 148,980	$ 1,356,470	$ 649,231	$ 417,843
Basic:
Income from continuing operations (USD per share)	$ 0.50	$ 0.44	$ 0.43	$ 0.44	$ 0.40	$ 0.43	$ 0.41	$ 0.37	$ 1.81	$ 1.61	$ 1.18
Net income attributable to common stockholders (USD per share)	1.10	1.72	0.43	0.56	0.59	0.43	0.42	0.44	3.82	1.88	1.26
Diluted:
Income from continuing operations (USD per share)	0.50	0.44	0.42	0.44	0.40	0.42	0.40	0.36	1.80	1.59	1.17
Net income attributable to common stockholders (USD per share)	1.09	1.71	0.42	0.55	0.58	0.42	0.42	0.44	3.78	1.86	1.25
Dividends declared per common share (in dollars per share)	$ 0.79	$ 0.775	$ 0.775	$ 0.775	$ 0.775	$ 0.73	$ 0.73	$ 0.73	$ 3.115	$ 2.965	$ 3.040