Dividends (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Jan. 15, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Dividends		$ 356,409	$ 333,692	$ 303,164
Dividends, Per share (in dollars per share)		$ 2.070	$ 2.030000	$ 1.950
Common stock dividends declared and paid (in dollars per share)		$ 2.07	$ 2.03	$ 1.95
Subsequent Event
Class of Stock [Line Items]
Common stock dividends declared and paid (in dollars per share)	$ 0.520
Series F Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid		$ 17,940	$ 17,940	$ 17,940
Preferred stock dividends declared and paid (in dollars per share)		$ 1.300000	$ 1.300000	$ 1.300000
Series E Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid		$ 0	$ 13,201	$ 16,387
Preferred stock dividends declared and paid (in dollars per share)			$ 1.147917	$ 1.425000
Ordinary dividends
Class of Stock [Line Items]
Dividends, Per share (in dollars per share)		$ 1.659755	1.762899	1.658604
Ordinary dividends | Series F Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid (in dollars per share)		1.300000	1.300000	1.255820
Ordinary dividends | Series E Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid (in dollars per share)			1.147917	1.376571
Capital gain
Class of Stock [Line Items]
Dividends, Per share (in dollars per share)		0	0	0.015534
Capital gain | Series F Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid (in dollars per share)		0	0	0.011761
Capital gain | Series E Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid (in dollars per share)			0	0.012892
Unrecaptured Section 1250 Gain
Class of Stock [Line Items]
Dividends, Per share (in dollars per share)		0	0	0.042818
Unrecaptured Section 1250 Gain | Series F Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid (in dollars per share)		0	0	0.032419
Unrecaptured Section 1250 Gain | Series E Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared and paid (in dollars per share)			0	0.035537
Nontaxable distributions
Class of Stock [Line Items]
Dividends, Per share (in dollars per share)		$ 0.410245	$ 0.267101	$ 0.233044