Stock Options And Employee Stock Purchase Plan (Stock Options) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Number of Shares, Outstanding Beginning of Period	707,777
Number of options granted	0
Number of Shares, Exercised	(155,538)
Number of Shares, Canceled	0
Number of Shares, Outstanding Ending of Period	552,239
Number of Shares, Exercisable	193,039
Number of Shares, Vested and expected to vest	420,068
Weighted-Average Exercise Price, Outstanding Beginning of Period	$ 56.84
Weighted-Average Exercise Price, Granted	0.00
Weighted-Average Exercise Price, Exercised	33.81
Weighted-Average Exercise Price, Canceled	0.00
Weighted-Average Exercise Price, Outstanding Ending of Period	63.33
Weighted-Average Exercise Price, Exercisable	41.91
Weighted-Average Exercise Price, Vested and expected to vest	$ 59.66
Weighted-Average Remaining Contractual Term, Outstanding (in years)	6 years 11 months 27 days
Weighted-Average Remaining Contractual Term, Exercisable (in years)	3 years 10 months 2 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest (in years)	6 years 5 months 9 days
Aggregate Intrinsic Value, Outstanding	$ 12,853,259
Aggregate Intrinsic Value, Exercisable	8,626,659
Aggregate Intrinsic Value, Vested and expected to vest	11,318,687
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value	8,000,000	$ 1,500,000
Allocated Share-based Compensation Expense	$ 5,086,000	$ 6,420,000
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Estimated Forfeiture Rate	12.63%	10.74%
Employee Stock Option [Member]
Allocated Share-based Compensation Expense	$ 200,000	$ 200,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	6 years 7 months 13 days