Stock-Based Compensation (Nonvested Performance-based Award Activity) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Non-Employee Directors [Member] | Deferred Compensation Plans [Member]
Non-vested PSU Awards [Roll Forward]
Granted at target level	14,579
Non-vested PSU Awards, Weighted Average Grant Date Fair Value [Roll Forward]
Granted at target level	$ 121.40
Incentive Stock Awards [Member]
Non-vested PSU Awards [Roll Forward]
Granted at target level	1,300	1,500	1,800
Forfeited	0	(200)	(800)
Non-vested PSU Awards, Weighted Average Grant Date Fair Value [Roll Forward]
Granted at target level	$ 106.14	$ 93.00	$ 86.93
Cash-settled PSU awards [Member]
Non-vested PSU Awards [Roll Forward]
Outstanding, beginning	1,592	1,972	2,451
Granted at target level	806	560	598
Adjustments above/(below) target	206	30	107
Vested and converted	(211)	(910)	(970)
Forfeited	0	0	0
Outstanding, ending	1,981	1,592	1,972
Non-vested PSU Awards, Weighted Average Grant Date Fair Value [Roll Forward]
Outstanding, beginning (in USD per share)	$ 79.48	$ 92.25	$ 25.28
Granted at target level	102.51	89.64	83.47
Adjustments above/(below) target	56.95	41.53	66.61
Vested and converted	102.51	93.00	86.93
Forfeited	0	0	0
Outstanding, ending (in USD per share)	$ 150.33	$ 79.48	$ 92.25
Stock-settled PSU awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares to be issued upon conversion	84,670
Average remaining term of shares issued at conversion	1 year
Non-vested PSU Awards [Roll Forward]
Outstanding, beginning	296,037	341,944	378,062
Granted at target level	84,309	102,307	92,045
Adjustments above/(below) target	50,556	2,284	11,369
Vested and converted	(48,964)	(121,984)	(116,684)
Forfeited	(16,204)	(23,946)	(110)
Outstanding, ending	264,622	296,037	341,944
Non-vested PSU Awards, Weighted Average Grant Date Fair Value [Roll Forward]
Outstanding, beginning (in USD per share)	$ 76.84	$ 64.38	$ 54.47
Granted at target level	103.40	90.45	84.01
Adjustments above/(below) target	83.89	33.86	42.85
Vested and converted	102.51	93.00	50.06
Forfeited	69.09	68.65	73.64
Outstanding, ending (in USD per share)	$ 66.03	$ 76.84	$ 64.38
Restricted Stock [Member]
Non-vested PSU Awards [Roll Forward]
Granted at target level	13,308	0
Non-vested PSU Awards, Weighted Average Grant Date Fair Value [Roll Forward]
Granted at target level	$ 116.39
Minimum [Member] | Cash-settled PSU awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Actual payout range	0.00%
Minimum [Member] | Stock-settled PSU awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Actual payout range	0.00%
Maximum [Member] | Cash-settled PSU awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Actual payout range	200.00%
Maximum [Member] | Stock-settled PSU awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Actual payout range	200.00%