Share-Based Compensation, Employee Stock Purchase Plan (Details) - USD ($) $ / shares in Units, $ in Millions		6 Months Ended						12 Months Ended
		Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercised, shares issued								51,658	72,707	62,866
Employee Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized		4,000,000.0						4,000,000.0
Maximum employee contribution rate		10.00%						10.00%
Employee stock purchase plan, purchase price								85.00%
Expected dividend yield								1.07%	1.36%	1.22%
Expected volatility								30.55%	17.43%	13.29%
Risk-free interest rate								1.01%	2.31%	1.73%
Expected term (years)								6 months	6 months	6 months
Weighted-average grant date fair value								$ 35.14	$ 21.56	$ 18.66
Compensation expense								$ 1.7	$ 1.4	$ 1.3
Shares available for future grants		3,400,000						3,400,000
July 2020 Offering ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercised, purchase price		$ 122.91
Exercised, shares issued		23,292
Proceeds received from employees	[1]	$ 2.9
January 2020 Offering ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercised, purchase price			$ 126.90
Exercised, shares issued			23,709
Proceeds received from employees	[1]		$ 3.0
July 2019 offering ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercised, purchase price				$ 104.83
Exercised, shares issued				27,949
Proceeds received from employees	[1]			$ 2.9
January 2019 offering ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercised, purchase price					$ 81.83
Exercised, shares issued					36,735
Proceeds received from employees	[1]				$ 3.0
July 2018 offering ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercised, purchase price						$ 81.13
Exercised, shares issued						35,972
Proceeds received from employees	[1]					$ 2.9
January 2018 offering ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercised, purchase price							$ 90.07
Exercised, shares issued							32,271
Proceeds received from employees	[1]						$ 2.9

[1] Represents amounts received from employees through payroll deductions for share purchases under applicable offering.