Net Income Per Share (Schedule of Computation of Net Income) (Loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net income	$ 25,994	$ 21,625	$ 28,327	$ 30,065	$ 29,381	$ 26,340	$ 20,186	$ 18,274	$ 106,011	$ 94,181	$ 75,410
Denominator:
Weighted-average shares used to compute basic net income per share (in shares)									115,412	114,349	115,343
Dilutive effect of employee stock options (in shares)									8,782	8,217	11,345
Weighted-average shares used to compute diluted net income per share (in shares)									124,194	122,566	126,688
Net income per share
Basic (in dollars per share)	$ 0.22	$ 0.19	$ 0.25	$ 0.26	$ 0.26	$ 0.23	$ 0.18	$ 0.16	$ 0.92	$ 0.82	$ 0.65
Diluted (in dollars per share)	$ 0.20	$ 0.17	$ 0.23	$ 0.25	$ 0.24	$ 0.22	$ 0.17	$ 0.15	$ 0.85	$ 0.77	$ 0.60