Stock-Based Compensation Restricted Stock Units Summary (Details) - Restricted Stock Units (RSUs) [Member] - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
[Line Items]
Outstanding, beginning balance (in shares)		544	684
Outstanding, beginning balance, weighted average grant date fair value (in dollars per share)		$ 71.79
Granted (in shares)		186	182
Granted, weighted average grant date fair value (in dollars per share)		$ 100.28	$ 87.17
Forfeited (in shares)		(10)	(7)
Forfeited, weighted average grant date fair value (in dollars per share)		$ 74.41
Outstanding, ending balance (in shares)		543	667
Outstanding, ending balance, weighted average grant date fair value (in dollars per share)		$ 81.03
Vested and Released [Member]
[Line Items]
Released (in shares)	[1]	(177)	(192)
Released, weighted average grant date fair value (in dollars per share)		$ 74.10
Released, aggregate intrinsic value		$ 18,007	$ 12,454
Vested but Not Released [Member]
[Line Items]
Released (in shares)		(10)
Released, aggregate intrinsic value		$ 845
Long Term Performance Restricted Stock Award [Member]
[Line Items]
Granted, weighted average grant date fair value (in dollars per share)		$ 113.75	$ 94.28

[1] (1)     Shares released is presented as gross shares and does not reflect shares withheld by us for employee payroll tax obligations.