Stock Options And Employee Stock Purchase Plan (Stock Options) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Shares, Outstanding Beginning of Period	566,428	725,649	1,175,657
Number of options granted	0	62,000	0
Number of Shares, Exercised	(142,870)	(221,221)	(433,008)
Number of Shares, Canceled	(9,700)	0	(17,000)
Number of Shares, Outstanding Ending of Period	413,858	566,428	725,649
Number of Shares, Exercisable	353,258	457,792	618,437
Number of Shares, Vested and expected to vest	402,809
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-Average Exercise Price, Outstanding Beginning of Period	$ 29.74	$ 24.29	$ 21.08
Weighted-Average Exercise Price, Granted	0.00	67.35	0.00
Weighted-Average Exercise Price, Exercised	26.04	22.41	15.70
Weighted-Average Exercise Price, Canceled	26.92	0.00	29.85
Weighted-Average Exercise Price, Outstanding Ending of Period	31.09	29.74	24.29
Weighted-Average Exercise Price, Exercisable	26.10	$ 24.78	$ 23.77
Weighted-Average Exercise Price, Vested and expected to vest	$ 30.14
Weighted-Average Remaining Contractual Term, Outstanding (in years)	3 years 9 months 26 days
Weighted-Average Remaining Contractual Term, Exercisable (in years)	3 years 1 month 21 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest (in years)	3 years 8 months 12 days
Aggregate Intrinsic Value, Outstanding	$ 20,988,138
Aggregate Intrinsic Value, Exercisable	19,676,668
Aggregate Intrinsic Value, Vested and expected to vest	$ 20,809,814