Quarterly Financial Information (Unaudited) (Summarized Unaudited Consolidated Quarterly Information) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 996,004	$ 983,155	$ 950,717	$ 942,874	$ 923,263	$ 936,538	$ 942,304	$ 943,705	$ 3,872,750	$ 3,745,810	$ 3,574,149
Income from continuing operations	12,893	86,918	211,898	127,588	63,302	103,281	169,300	80,108	439,297	415,991	1,361,222
Discontinued operations					0	0	0	(10)	0	(10)	(110)
Net income	12,893	86,918	211,898	127,588	63,302	103,281	169,300	80,098	439,297	415,981	1,361,112
Net income attributable to noncontrolling interests	1,450	1,659	1,369	1,803	1,029	1,309	2,781	1,395	6,281	6,514	4,642
Net income attributable to common stockholders	$ 11,443	$ 85,259	$ 210,529	$ 125,785	$ 62,273	$ 101,972	$ 166,519	$ 78,703	$ 433,016	$ 409,467	$ 1,356,470
Basic:
Income from continuing operations (USD per share)	$ 0.03	$ 0.23	$ 0.59	$ 0.36	$ 0.18	$ 0.29	$ 0.48	$ 0.22	$ 1.20	$ 1.17	$ 3.83
Net income attributable to common stockholders (USD per share)	0.03	0.23	0.58	0.35	0.17	0.29	0.47	0.22	1.18	1.15	3.82
Diluted:
Income from continuing operations (USD per share)	0.03	0.23	0.58	0.35	0.18	0.29	0.47	0.22	1.19	1.16	3.80
Net income attributable to common stockholders (USD per share)	0.03	0.23	0.58	0.35	0.17	0.28	0.46	0.22	1.17	1.14	3.78
Dividends declared per common share (in dollars per share)		$ 0.7925	$ 0.7925	$ 0.7925	$ 0.7925	$ 0.79	$ 0.79	$ 0.79	$ 3.17000	3.16250	3.11500
Common Stock, Dividends, Per Share, Declared, Taxable in Following Year	$ 0.79250									$ 0.79250	$ 0.79000