Net Income Per Share (Computation Of Basic And Diluted Net Income Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator for basic and diluted net income per share:
Net income	$ 1,903	$ 2,124	$ 10,924	$ 11,019	$ 8,989	$ 9,063	$ 20,278	$ 16,057	$ 25,970	$ 54,387	$ 15,902
Denominator for basic net income per share:
Weighted-average common shares outstanding (in shares)	39,853	39,853	39,853	39,823	38,447	39,641	37,419	37,025	39,846	38,447	36,404
Basic net income per share (in dollars per share)	$ 0.05	$ 0.05	$ 0.27	$ 0.28	$ 0.23	$ 0.23	$ 0.54	$ 0.43	$ 0.65	$ 1.41	$ 0.44
Denominator for diluted net income per share:
Dilutive stock options, restricted stock and performance restricted stock units and employee stock purchase plan shares (in shares)									588	968	806
Diluted weighted-average common shares outstanding (in shares)	40,340	40,492	40,412	40,480	39,415	40,264	38,613	38,441	40,434	39,415	37,210
Diluted net income per share (in dollars per share)	$ 0.05	$ 0.05	$ 0.27	$ 0.27	$ 0.23	$ 0.23	$ 0.53	$ 0.42	$ 0.64	$ 1.38	$ 0.43
Common stock
Denominator for basic net income per share:
Weighted-average common shares outstanding (in shares)									39,846	38,447	36,404