Share-Based Compensation - Option Rollforward (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Roll [Forward]
Beginning Balance	144,412
Options Granted	49,115	51,610	35,842	42,477
Options Exercised	(83,191)
Ending Balance	110,336	144,412
Options Expected to Vest	92,890
Options Exerciseable	17,446
Weighted Average Exercise Price [Abstract]
Outstanding at beginning of year	$ 137.15
Options Granted	136.64
Options Exercised	128.42
Outstanding at End of Period	143.51	$ 137.15
Options Expected to Vest	144.86
Options Exerciseable	$ 136.32
Share Based Compensation Arrangement By Share Based Payment Award Options Additional Disclosures [Abstract]
Weighted Average Remaining Contractual Term, Outstanding	5 years 2 months 12 days
Weighted Average Remaining Contractual Term, Expected to Vest	5 years 7 months 6 days
Weighted Average Remaining Contractual Term, Exercisable	3 years 4 months 24 days
Outstanding Options, Intrinsic Value	$ 12,015
Expected to Vest Options, Intrinsic Value	9,990
Exercisable Options, Intrinsic Value	$ 2,025