Stock Options And Employee Stock Purchase Plan (Stock Options) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Number of Shares, Outstanding Beginning of Period			566,428
Number of options granted			0
Number of Shares, Exercised			(71,058)
Number of Shares, Canceled			(9,700)
Number of Shares, Outstanding Ending of Period	485,670		485,670
Number of Shares, Exercisable	421,570		421,570
Number of Shares, Vested and expected to vest	471,653		471,653
Weighted-Average Exercise Price, Outstanding Beginning of Period			$ 29.74
Weighted-Average Exercise Price, Granted			0.00
Weighted-Average Exercise Price, Exercised			26.38
Weighted-Average Exercise Price, Canceled			26.92
Weighted-Average Exercise Price, Outstanding Ending of Period	$ 30.29		30.29
Weighted-Average Exercise Price, Exercisable	26.00		26.00
Weighted-Average Exercise Price, Vested and expected to vest	$ 29.29		$ 29.29
Weighted-Average Remaining Contractual Term, Outstanding (in years)			4 years 11 days
Weighted-Average Remaining Contractual Term, Exercisable (in years)			3 years 4 months 24 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest (in years)			3 years 10 months 24 days
Aggregate Intrinsic Value, Outstanding	$ 16,228,340		$ 16,228,340
Aggregate Intrinsic Value, Exercisable	15,721,070		15,721,070
Aggregate Intrinsic Value, Vested and expected to vest	16,185,217		16,185,217
Aggregate intrinsic values of options exercised			2,500,000	$ 5,600,000
Allocated Share-based Compensation Expense	3,439,000	$ 3,168,000	$ 6,248,000	$ 6,173,000
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Estimated Forfeiture Rate			12.33%	13.42%
Stock Options [Member]
Allocated Share-based Compensation Expense			$ 200,000	$ 500,000
Unrecognized compensation cost related to non-vested awards granted	$ 800,000		$ 800,000		$ 1,100,000
Weighted-average period to recognize compensation cost (in years)			3 years 1 month 28 days