Stock Options And Employee Stock Purchase Plan (Narrative) (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Allocated Share-based Compensation Expense	$ 3,004,000	$ 2,384,000
Number of options outstanding	722,849		725,649
Number of options granted	0
Cash received upon the issuance of common stock	61,000	55,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value	100,000	12,300,000
Stock Options [Member]
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	600,000		800,000
Restricted Stock And Restricted Stock Unit (RSU) [Member]
Allocated Share-based Compensation Expense	3,000,000	1,900,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	28,500,000		24,100,000
Restricted Stock [Member]
Shares, Granted	24,000
Weighted-Average Grant-Date Fair Value, Granted	$ 59.86
Number of stocks outstanding	784,062		814,050
Restricted Stock Units (RSUs) [Member]
Shares, Granted	8,000
Number of stocks outstanding	106,294		102,294
1997 Stock Option Plan [Member]
Additional shares authorized for issuance	840,000
Maximum issuance of common stock	12,000,000
1997 Stock Option Plan [Member] | Stock Options [Member]
Number of options outstanding	222,706
1997 Stock Option Plan [Member] | Restricted Stock [Member]
Number of stocks outstanding	0
2007 Stock Plan [Member]
Number of options outstanding	500,143
Number of stocks outstanding	106,924
Maximum issuance of common stock	4,500,000
Employee Stock Purchase Plan [Member] | Common Stock [Member]
Market value of common stock on the date of grant for incentive stock options	95.00%
Maximum earnings withheld by the employees	15.00%
Number of shares purchased under the plan	1,114	1,270
Cash received upon the issuance of common stock	$ 61,000	$ 55,000
Number of shares available for issuance	1,633,350
Minimum [Member]
Market value of common stock on the date of grant for incentive stock options	85.00%