Common and Preferred Shares Common Shares (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares
Cash Dividends Paid [Line Items]
shelf registration effective term	3
Stock Repurchase Program, Number of Shares Authorized to be Repurchased | shares	15,000,000
Common Stock, Dividends, Per Share, Cash Paid	$ 4.50	$ 4.32	$ 4.08
Common Stock, Shares, Issued | shares	81,588,489	77,226,443
Net proceeds from issuance of common shares | $	$ 305,556	$ 956	$ 99,069
Common Stock [Member]
Cash Dividends Paid [Line Items]
Common stock declared dividends per share	$ 4.50	$ 4.32
Total Cash Distribution Per Share [Member] | Common Stock [Member]
Cash Dividends Paid [Line Items]
Common Stock, Dividends, Per Share, Cash Paid	4.4850	4.3000
Taxable Ordinary Income [Member] | Common Stock [Member]
Cash Dividends Paid [Line Items]
Common Stock, Dividends, Per Share, Cash Paid	2.7411	4.1253
Return of Capital [Member] | Common Stock [Member]
Cash Dividends Paid [Line Items]
Common Stock, Dividends, Per Share, Cash Paid	1.3966	0
Long-term Capital Gain [Member] | Common Stock [Member]
Cash Dividends Paid [Line Items]
Common Stock, Dividends, Per Share, Cash Paid	0.3473	0.1747
Unrecaptured Section 1250 gain	$ 0.3473	$ 0.0102
direct share purchase plan [Member]
Cash Dividends Paid [Line Items]
Common Stock, Shares, Issued | shares	4,007,113
Net proceeds from issuance of common shares | $	$ 305,900