Quarterly Financial Information (Unaudited) (Summarized Unaudited Consolidated Quarterly Information) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 875,713	$ 867,116	$ 848,404	$ 852,289	$ 841,274	$ 827,606	$ 811,920	$ 805,598	$ 3,443,522	$ 3,286,398	$ 2,776,813
Income from continuing operations attributable to common stockholders, including real estate dispositions	207,804	149,570	143,310	149,469	127,059	45,235	131,578	102,868	554,209	389,539	359,296
Discontinued operations	(167)	(118)	(148)	(489)	(2,331)	(22,383)	18,243	17,574	(922)	11,103	99,735
Net income attributable to common stockholders	$ 207,637	$ 149,452	$ 143,162	$ 148,980	$ 124,728	$ 22,852	$ 149,821	$ 120,442	$ 649,231	$ 417,843	$ 475,767
Basic:
Income from continuing operations attributable to common stockholders, including real estate dispositions (USD per share)	$ 0.59	$ 0.43	$ 0.42	$ 0.44	$ 0.38	$ 0.14	$ 0.39	$ 0.32	$ 1.88	$ 1.23	$ 1.28
Discontinued operations (USD per share)	0.00	0.00	0.00	0.00	(0.01)	(0.07)	0.06	0.05	0.00	0.03	0.34
Net income attributable to common stockholders (USD per share)	0.59	0.43	0.42	0.44	0.37	0.07	0.45	0.37	1.88	1.26	1.62
Diluted:
Income from continuing operations attributable to common stockholders, including real estate dispositions (USD per share)	0.58	0.42	0.42	0.44	0.38	0.14	0.40	0.32	1.86	1.22	1.26
Discontinued operations (USD per share)	0.00	0.00	0.00	0.00	(0.01)	(0.07)	0.05	0.05	0.00	0.03	0.34
Net income attributable to common stockholders (USD per share)	0.58	0.42	0.42	0.44	0.37	0.07	0.45	0.37	$ 1.86	$ 1.25	$ 1.60
Dividends declared per common share (in dollars per share)	$ 0.775	$ 0.730	$ 0.730	$ 0.730	$ 0.73000	$ 0.73000	$ 0.79000	$ 0.79000