Stock Options And Employee Stock Purchase Plan (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Allocated Share-based Compensation Expense	$ 2,770,000	$ 2,191,000	$ 8,943,000	$ 6,538,000
Number of options outstanding	582,028		582,028		725,649
Number of options granted			62,000
Cash received upon the issuance of common stock			$ 196,000	199,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value			9,600,000	14,500,000
Stock Options [Member]
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	$ 1,200,000		1,200,000		$ 800,000
Restricted Stock And Restricted Stock Unit (RSU) [Member]
Allocated Share-based Compensation Expense			8,300,000	$ 5,500,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	$ 35,600,000		$ 35,600,000		$ 24,100,000
Restricted Stock [Member]
Shares, Granted			211,040
Weighted-Average Grant-Date Fair Value, Granted			$ 67.06
Number of stocks outstanding	784,842		784,842		814,050
Restricted Stock Units (RSUs) [Member]
Shares, Granted			15,900
Number of stocks outstanding	64,685		64,685		102,924
1997 Stock Option Plan [Member]
Additional shares authorized for issuance			840,000
Maximum issuance of common stock	12,000,000		12,000,000
1997 Stock Option Plan [Member] | Stock Options [Member]
Number of options outstanding	65,498		65,498
1997 Stock Option Plan [Member] | Restricted Stock [Member]
Number of stocks outstanding	0		0
2007 Stock Plan [Member]
Number of options outstanding	454,530		454,530
Number of stocks outstanding	59,685		59,685
Maximum issuance of common stock	4,500,000		4,500,000
2015 Stock Option Plan [Member]
Number of options outstanding	62,000		62,000
Number of stocks outstanding	5,000		5,000
Maximum issuance of common stock	4,200,000		4,200,000
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%		15.00%
Number of shares purchased under the plan			3,155	4,463
Cash received upon the issuance of common stock			$ 196,000	$ 199,000
Number of shares available for issuance	1,631,309		1,631,309
Minimum [Member]
Market value of common stock on the date of grant for incentive stock options			85.00%