Share-Based Compensation - Non-employee Director Option Plan (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement By Share-based Payment Award, Fair Value Assumptions, Percent Expected To Vest	62.10%	57.60%	65.50%	75.60%
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted shares	290,607	261,731	190,020
Weighted Average Grant Date Fair Value	$ 131.84	$ 144.89	$ 107.50
Director Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares Authorized	375,000
Number of Shares Available for Grant	169,865
Two Thousand Fifteen Equity Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares Authorized	1,750,000
Number of Shares Available for Grant	457,767
Executive Officer [Member] | Two Thousand Fifteen Equity Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award Vesting Rights, Percentage		100.00%
Executive Officer [Member] | Two Thousand Fifteen Equity Plan [Member] | Time Based [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award Vesting Rights, Percentage	20.00%
Award Vesting Period	5 years
Director [Member] | 2004 Non-employee Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award Vesting Rights, Percentage		100.00%
Time Based [Member] | Director [Member] | 2004 Non-employee Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Average Grant Date Fair Value		$ 147.97
Time Based [Member] | Key Employees [Member] | Two Thousand Fifteen Equity Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted shares		1,500
Weighted Average Grant Date Fair Value		$ 143.20
Market Condition [Member] | Executive Officer [Member] | Two Thousand Fifteen Equity Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted shares		69,000
Weighted Average Grant Date Fair Value		$ 125.47
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Price	$ 151.89	151.89	$ 147.19	$ 165.97
Award Date One [Member] | Director [Member] | 2004 Non-employee Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award Vesting Rights, Percentage	100.00%
Award Date One [Member] | Key Employees [Member] | Two Thousand Fifteen Equity Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Average Grant Date Fair Value		$ 162.42
Award Date One [Member] | Time Based [Member] | Director [Member] | 2004 Non-employee Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted shares	10,200
Weighted Average Grant Date Fair Value	$ 148.44
Award Date One [Member] | Time Based [Member] | Key Employees [Member] | Two Thousand Fifteen Equity Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted shares		51,790
Award Date Two [Member] | Director [Member] | 2004 Non-employee Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award Vesting Rights, Percentage	100.00%
Award Date Two [Member] | Time Based [Member] | Director [Member] | 2004 Non-employee Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted shares	1,509
Weighted Average Grant Date Fair Value	$ 147.19
Award Date Two [Member] | Time Based [Member] | Key Employees [Member] | Two Thousand Fifteen Equity Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted shares		13,873
Weighted Average Grant Date Fair Value		$ 140.39
Award Date Three [Member] | Executive Officer [Member] | Two Thousand Fifteen Equity Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award Vesting Rights, Percentage	100.00%
Award Date Three [Member] | Market Condition [Member] | Executive Officer [Member] | Two Thousand Fifteen Equity Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted shares	5,100
Weighted Average Grant Date Fair Value	$ 96.41
Award Date Four | Time Based [Member] | Executive Officer [Member] | Two Thousand Fifteen Equity Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted shares	3,400	69,368
Weighted Average Grant Date Fair Value	$ 147.19	$ 137.63
Award Vesting Rights, Percentage	20.00%
Award Vesting Period	5 years
Award Date Five | Key Employees [Member] | Two Thousand Fifteen Equity Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Average Grant Date Fair Value	$ 143.28
Award Vesting Rights, Percentage	20.00%
Award Vesting Period	5 years
Award Date Five | Time Based [Member] | Executive Officer [Member] | Two Thousand Fifteen Equity Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted shares		46,000
Weighted Average Grant Date Fair Value		$ 165.97
Award Date Five | Time Based [Member] | Director [Member] | 2004 Non-employee Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted shares		10,200
Award Date Five | Time Based [Member] | Key Employees [Member] | Two Thousand Fifteen Equity Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted shares	61,550
Award Date Six | Key Employees [Member] | Two Thousand Fifteen Equity Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Average Grant Date Fair Value	$ 151.89
Award Vesting Rights, Percentage	33.30%
Award Vesting Period	3 years
Award Date Six | Time Based [Member] | Key Employees [Member] | Two Thousand Fifteen Equity Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted shares	28,856
Award Date Seven | Executive Officer [Member] | Two Thousand Fifteen Equity Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award Vesting Rights, Percentage	100.00%
Award Date Seven | Market Condition [Member] | Executive Officer [Member] | Two Thousand Fifteen Equity Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted shares	15,000
Weighted Average Grant Date Fair Value	$ 87.49
Award Date Eight | Time Based [Member] | Executive Officer [Member] | Two Thousand Fifteen Equity Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted shares	15,000
Weighted Average Grant Date Fair Value	$ 151.89
Award Vesting Rights, Percentage	33.30%
Award Vesting Period	3 years
Award Date Nine | Executive Officer [Member] | Two Thousand Fifteen Equity Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award Vesting Rights, Percentage	100.00%
Award Date Nine | Market Condition [Member] | Executive Officer [Member] | Two Thousand Fifteen Equity Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted shares	81,000
Weighted Average Grant Date Fair Value	$ 94.32
Award Date Ten | Time Based [Member] | Executive Officer [Member] | Two Thousand Fifteen Equity Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted shares	54,000
Weighted Average Grant Date Fair Value	$ 151.89
Award Vesting Rights, Percentage	20.00%
Award Vesting Period	5 years
Award Date Eleven | Time Based [Member] | Executive Officer [Member] | Two Thousand Fifteen Equity Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted shares	11,488
Weighted Average Grant Date Fair Value	$ 196.39
Award Vesting Rights, Percentage	20.00%
Award Vesting Period	5 years
Award Date Twelve | Key Employees [Member] | Two Thousand Fifteen Equity Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Average Grant Date Fair Value	$ 202.31
Award Vesting Rights, Percentage	25.00%
Award Vesting Period	4 years
Award Date Twelve | Time Based [Member] | Key Employees [Member] | Two Thousand Fifteen Equity Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted shares	1,004
Award Date Thirteen | Key Employees [Member] | Two Thousand Fifteen Equity Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Average Grant Date Fair Value	$ 196.75
Award Vesting Rights, Percentage	20.00%
Award Vesting Period	5 years
Award Date Thirteen | Time Based [Member] | Key Employees [Member] | Two Thousand Fifteen Equity Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted shares	2,500