Stock Compensation Plans and Other Employee Benefit Plans (Summary of Plans' Restricted Share Award Activity) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restricted Shares
Common Shares
Outstanding at the beginning of period (in shares)	143,263	127,787	133,425
Granted (in shares)	24,285	35,654	16,552
Vested and issued (in shares)	(21,529)	(18,324)	(19,639)
Forfeited or canceled (in shares)	(1,691)	(1,854)	(2,551)
Outstanding at the end of period (in shares)	144,328	143,263	127,787
Vested, but not issuable, or deferred, at year end (in shares)	92,183	90,520	89,723
Weighted Average Grant-Date Fair Value
Outstanding at beginning of the period (in dollars per share)	$ 60.80	$ 53.33	$ 49.94
Granted (in dollars per share)	68.58	84.36	73.16
Vested and issued (in dollars per share)	70.99	54.31	47.13
Forfeited or canceled (in dollars per share)	79.50	63.50	52.26
Outstanding at end of the period (in dollars per share)	60.37	60.80	53.33
Vested, but not issuable, or deferred, at year end (in dollars per share)	$ 52.24	$ 51.94	$ 51.64
Performance Shares
Common Shares
Outstanding at the beginning of period (in shares)	396,855	359,196	298,180
Granted (in shares)	175,823	134,380	145,853
Added by performance factor at vesting (in shares)	33,950	0	0
Vested and issued (in shares)	(128,238)	(82,307)	(68,712)
Forfeited or canceled (in shares)	(12,875)	(14,414)	(16,125)
Outstanding at the end of period (in shares)	465,515	396,855	359,196
Vested, but not issuable, or deferred, at year end (in shares)	33,828	21,530	108,143,000
Weighted Average Grant-Date Fair Value
Outstanding at beginning of the period (in dollars per share)	$ 67.71	$ 54.37	$ 43.64
Granted (in dollars per share)	71.56	88.27	72.60
Added by performance factor at vesting (in dollars per share)	40.99	0	0
Vested and issued (in dollars per share)	41.00	44.39	46.85
Forfeited or canceled (in dollars per share)	75.08	60.05	52.98
Outstanding at end of the period (in dollars per share)	74.37	67.71	54.37
Vested, but not issuable, or deferred, at year end (in dollars per share)	$ 43.01	$ 43.54	$ 44.16