Earnings Per Share (Narrative) (Details) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Anitidlutive securities exluded from computation of earnings per share [Line Items]
Exercise price range, lower limit	$ 61.79		$ 51.64
Exercise price range, upper limit	$ 76.63	$ 61.79	$ 65.50
Series C Cumulative Convertible Preferred Share [Member]
Anitidlutive securities exluded from computation of earnings per share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	2,100	2,000	2,000
Preferred share dividend percentage	5.75%
Series E Cumulative Convertible Preferred Share [Member]
Anitidlutive securities exluded from computation of earnings per share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	1,600	1,600	1,600
Preferred share dividend percentage	9.00%
Stock Options [Member]
Anitidlutive securities exluded from computation of earnings per share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	7	72	236