Common and Preferred Shares Preferred Shares (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 21, 2017
Schedule of Preferred Stock [Line Items]
Proceeds from Issuance of Preferred Stock and Preference Stock	$ 0	$ 144,490	$ 0
Preferred Share Redemption Costs	$ 0	$ 4,457	$ 0
Series C Preferred Shares [Member]
Schedule of Preferred Stock [Line Items]
Preferred Stock, Shares Issued	5,394,050	5,399,050
Preferred share dividend percentage	5.75%
Preferred share dividend rate (in dollars per share)	$ 1.4375
Per share liquidation preference	25
Preferred shares conversion rate	0.3954
Preferred shares conversion price	63.23
Common shares quarterly dividend per share threshold, minimum	$ 0.6875
Common share closing price percent of preferred share prevailing conversion price, minimum	135.00%
Preferred Shares declared dividends per share	$ 1.4375	$ 1.4375
Preferred Shares, Convertible, Conversion Adjustment	$ 0.6205	$ 0.4918
Series E Preferred Shares [Member]
Schedule of Preferred Stock [Line Items]
Preferred Stock, Shares Issued	3,447,381	3,449,115
Preferred share dividend percentage	9.00%
Preferred share dividend rate (in dollars per share)	$ 2.25
Per share liquidation preference	25
Preferred shares conversion rate	0.4686
Preferred shares conversion price	53.35
Common shares quarterly dividend per share threshold, minimum	$ 0.84
Common share closing price percent of preferred share prevailing conversion price, minimum	150.00%
Preferred Shares declared dividends per share	$ 2.25	$ 2.25
Preferred Shares, Convertible, Conversion Adjustment	$ 0.5308	$ 0.2619
Series F Preferred Stock [Member]
Schedule of Preferred Stock [Line Items]
Preferred Stock, Shares Issued				5,000,000
Preferred share dividend percentage		6.625%
Preferred Stock, Redemption Price Per Share		$ 25.299045
Per share liquidation preference		$ 25.00
Preferred Stock, Redemption Amount		$ 126,500
Preferred Shares declared dividends per share		$ 1.54123
Preferred Stock, Dividends, Per Share, Cash Paid		$ 0.299045
Preferred Share Redemption Costs		$ 4,500
Series G Preferred Stock [Member]
Schedule of Preferred Stock [Line Items]
Preferred Stock, Shares Issued	6,000,000	6,000,000
Preferred share dividend percentage	5.75%
Proceeds from Issuance of Preferred Stock and Preference Stock		$ 144,500
Preferred share dividend rate (in dollars per share)	$ 1.4375
Per share liquidation preference	25
Preferred Shares declared dividends per share	0.183681
Taxable Ordinary Income [Member] | Series C Preferred Shares [Member]
Schedule of Preferred Stock [Line Items]
Dividends, per share, cash paid, taxable ordinary income, 199A distribution	1.3791
Preferred Stock, Dividends, Per Share, Non-cash Distributions	0.5953	$ 0.3527
Dividends, per share, non-cash distribution, taxable ordinary income, 199A distribution	0.5953
Preferred Stock, Dividends, Per Share, Cash Paid	1.3791	1.3462
Taxable Ordinary Income [Member] | Series E Preferred Shares [Member]
Schedule of Preferred Stock [Line Items]
Dividends, per share, cash paid, taxable ordinary income, 199A distribution	2.1586
Preferred Stock, Dividends, Per Share, Non-cash Distributions	0.5092	0.1428
Dividends, per share, non-cash distribution, taxable ordinary income, 199A distribution	0.5092
Preferred Stock, Dividends, Per Share, Cash Paid	2.1586	2.1070
Taxable Ordinary Income [Member] | Series F Preferred Stock [Member]
Schedule of Preferred Stock [Line Items]
Preferred Stock, Dividends, Per Share, Cash Paid		1.8310
Taxable Ordinary Income [Member] | Series G Preferred Stock [Member]
Schedule of Preferred Stock [Line Items]
Dividends, per share, cash paid, taxable ordinary income, 199A distribution	1.2105
Preferred Stock, Dividends, Per Share, Cash Paid	1.2105
Return of Capital [Member] | Series C Preferred Shares [Member]
Schedule of Preferred Stock [Line Items]
Preferred Stock, Dividends, Per Share, Non-cash Distributions	0.0000	0.1152
Preferred Stock, Dividends, Per Share, Cash Paid	0.0000	0.0000
Return of Capital [Member] | Series E Preferred Shares [Member]
Schedule of Preferred Stock [Line Items]
Preferred Stock, Dividends, Per Share, Non-cash Distributions	0.0000	0.1094
Preferred Stock, Dividends, Per Share, Cash Paid	0.0000	0.0000
Return of Capital [Member] | Series F Preferred Stock [Member]
Schedule of Preferred Stock [Line Items]
Preferred Stock, Dividends, Per Share, Cash Paid		0.0000
Return of Capital [Member] | Series G Preferred Stock [Member]
Schedule of Preferred Stock [Line Items]
Preferred Stock, Dividends, Per Share, Cash Paid	0.0000
Long-term Capital Gain [Member] | Series C Preferred Shares [Member]
Schedule of Preferred Stock [Line Items]
Preferred Stock, Dividends, Per Share, Non-cash Distributions	0.0252	0.0239
Unrecaptured Section 1250 gain	0.0034	0.0352
Dividends, Per Share, Non-cash Distributions, Unrecaptured Section 1250 Gain	0.0015	0.0092
Preferred Stock, Dividends, Per Share, Cash Paid	0.0584	0.0913
Long-term Capital Gain [Member] | Series E Preferred Shares [Member]
Schedule of Preferred Stock [Line Items]
Preferred Stock, Dividends, Per Share, Non-cash Distributions	0.0216	0.0097
Unrecaptured Section 1250 gain	0.0053	0.0551
Dividends, Per Share, Non-cash Distributions, Unrecaptured Section 1250 Gain	0.0013	0.0037
Preferred Stock, Dividends, Per Share, Cash Paid	0.0914	0.1430
Long-term Capital Gain [Member] | Series F Preferred Stock [Member]
Schedule of Preferred Stock [Line Items]
Unrecaptured Section 1250 gain		0.04792
Preferred Stock, Dividends, Per Share, Cash Paid		0.1243
Long-term Capital Gain [Member] | Series G Preferred Stock [Member]
Schedule of Preferred Stock [Line Items]
Dividends, Per Share, Non-cash Distributions, Unrecaptured Section 1250 Gain	0.002978
Preferred Stock, Dividends, Per Share, Cash Paid	0.0513
Total Cash Distribution Per Share [Member] | Series C Preferred Shares [Member]
Schedule of Preferred Stock [Line Items]
Preferred Stock, Dividends, Per Share, Cash Paid	1.4375	1.4375
Total Cash Distribution Per Share [Member] | Series E Preferred Shares [Member]
Schedule of Preferred Stock [Line Items]
Preferred Stock, Dividends, Per Share, Cash Paid	2.2500	2.2500
Total Cash Distribution Per Share [Member] | Series F Preferred Stock [Member]
Schedule of Preferred Stock [Line Items]
Preferred Stock, Dividends, Per Share, Cash Paid		1.9553
Total Cash Distribution Per Share [Member] | Series G Preferred Stock [Member]
Schedule of Preferred Stock [Line Items]
Preferred Stock, Dividends, Per Share, Cash Paid	1.2618
Total non-cash Distributions Per Share [Domain] | Series C Preferred Shares [Member]
Schedule of Preferred Stock [Line Items]
Preferred Stock, Dividends, Per Share, Non-cash Distributions	0.6205	0.4918
Total non-cash Distributions Per Share [Domain] | Series E Preferred Shares [Member]
Schedule of Preferred Stock [Line Items]
Preferred Stock, Dividends, Per Share, Non-cash Distributions	$ 0.5308	$ 0.2619