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, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net income	$ 29,381	$ 26,340	$ 20,186	$ 18,274	$ 22,008	$ 17,747	$ 18,196	$ 17,459	$ 94,181	$ 75,410	$ 129,122
Denominator:
Weighted-average shares used to compute basic net income per share (in shares)									114,349	115,343	113,527
Dilutive effect of employee stock options (in shares)									8,217	11,345	10,988
Weighted-average shares used to compute diluted net income per share (in shares)									122,566	126,688	124,515
Net income per share
Basic (in dollars per share)	$ 0.26	$ 0.23	$ 0.18	$ 0.16	$ 0.19	$ 0.15	$ 0.16	$ 0.15	$ 0.82	$ 0.65	$ 1.14
Diluted (in dollars per share)	$ 0.24	$ 0.22	$ 0.17	$ 0.15	$ 0.18	$ 0.14	$ 0.14	$ 0.14	$ 0.77	$ 0.60	$ 1.04