Stock Options And Employee Stock Purchase Plan (Stock Options) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Estimated Forfeiture Rate			14.43%	12.33%
Allocated Share-based Compensation Expense	$ 5,562,000	$ 3,439,000	$ 9,177,000	$ 6,248,000
Number of Shares, Outstanding Beginning of Period			413,858
Number of options granted			0
Number of Shares, Exercised			(36,183)
Number of Shares, Canceled			0
Number of Shares, Outstanding Ending of Period	377,675		377,675
Number of Shares, Exercisable	338,475		338,475
Number of Shares, Vested and expected to vest	368,546		368,546
Weighted-Average Exercise Price, Outstanding Beginning of Period			$ 31.09
Weighted-Average Exercise Price, Granted			0.00
Weighted-Average Exercise Price, Exercised			29.05
Weighted-Average Exercise Price, Canceled			0.00
Weighted-Average Exercise Price, Outstanding Ending of Period	$ 31.28		31.28
Weighted-Average Exercise Price, Exercisable	27.33		27.33
Weighted-Average Exercise Price, Vested and expected to vest	$ 30.39		$ 30.39
Weighted-Average Remaining Contractual Term, Outstanding (in years)			3 years 7 months 10 days
Weighted-Average Remaining Contractual Term, Exercisable (in years)			3 years 1 month 17 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest (in years)			3 years 6 months
Aggregate Intrinsic Value, Outstanding	$ 20,322,158		$ 20,322,158
Aggregate Intrinsic Value, Exercisable	19,549,090		19,549,090
Aggregate Intrinsic Value, Vested and expected to vest	20,158,778		$ 20,158,778
Employee Stock Option [Member]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition			2 years 8 months 16 days
Allocated Share-based Compensation Expense	$ 50,000	$ 100,000	$ 100,000	$ 200,000