Supplementary Quarterly Financial Data (Supplementary Quarterly Financial Data) (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
Supplementary Quarterly Financial Data [Abstract]
Self-storage and ancillary revenues	$ 717,499	$ 729,336	$ 710,950	$ 689,038	$ 692,460	$ 706,368	$ 685,528	$ 669,924	$ 2,846,823	$ 2,754,280	$ 2,668,528
Self storage and ancillary cost of operations	172,584	212,262	207,736	204,201	160,374	195,544	190,977	192,827
Depreciation and amortization	134,885	129,233	126,859	121,941	121,374	124,516	119,777	117,979	512,918	483,646	454,526
Net income	$ 387,097	$ 399,420	$ 371,456	$ 367,678	$ 587,906	$ 379,589	$ 405,292	$ 344,436	$ 1,525,651	$ 1,717,223	$ 1,448,465
Net income - Basic	$ 1.88	$ 1.94	$ 1.76	$ 1.73	$ 3.05	$ 1.85	$ 2.00	$ 1.66	$ 7.30	$ 8.56	$ 6.75
Net income - Diluted	$ 1.87	$ 1.93	$ 1.76	$ 1.73	$ 3.04	$ 1.85	$ 2.00	$ 1.65	$ 7.29	$ 8.54	$ 6.73