Stock Compensation Plans and Other Employee Benefit Plans (Summary of Plans' Restricted Share Award Activity) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restricted shares
Common Shares
Outstanding at the beginning of period (in shares)	127,787	133,425	137,593
Granted (in shares)	35,654	16,552	18,022
Vested and issued (in shares)	(18,324)	(19,639)	(20,007)
Forfeited (in shares)	(1,854)	(2,551)	(2,183)
Outstanding at the end of period (in shares)	143,263	127,787	133,425
Vested, but not issuable, or deferred, at year end (in shares)	90,520	89,723	89,050
Weighted Average Grant-Date Fair Value
Outstanding at beginning of the period (in dollars per share)	$ 53.33	$ 49.94	$ 49.63
Granted (in dollars per share)	84.36	73.16	46.01
Vested and issued (in dollars per share)	54.31	47.13	44.91
Forfeited (in dollars per share)	63.50	52.26	44.18
Outstanding at end of the period (in dollars per share)	60.80	53.33	49.94
Vested, but not issuable, or deferred, at year end (in dollars per share)	$ 51.94	$ 51.64	$ 51.47
Performance shares
Common Shares
Outstanding at the beginning of period (in shares)	359,196	298,180	276,533
Granted (in shares)	134,380	145,853	118,084
Vested and issued (in shares)	(82,307)	(68,712)	(78,410)
Forfeited (in shares)	(14,414)	(16,125)	(18,027)
Outstanding at the end of period (in shares)	396,855	359,196	298,180
Vested, but not issuable, or deferred, at year end (in shares)	21,530	108,143	6,672,000
Weighted Average Grant-Date Fair Value
Outstanding at beginning of the period (in dollars per share)	$ 54.37	$ 43.64	$ 43.01
Granted (in dollars per share)	88.27	72.60	41.02
Vested and issued (in dollars per share)	44.39	46.85	37.90
Forfeited (in dollars per share)	60.05	52.98	41.83
Outstanding at end of the period (in dollars per share)	67.71	54.37	43.64
Vested, but not issuable, or deferred, at year end (in dollars per share)	$ 43.54	$ 44.16	$ 37.98