Net Income Per Share - (Basic and Diluted Net Income Per Share) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Earnings Per Share [Abstract]
Net income	$ 6,318us-gaap_NetIncomeLoss	$ 6,194us-gaap_NetIncomeLoss
Weighted-average shares outstanding — basic	36,024	35,225
Add: Dilutive effect of employee stock plans (in shares)	890	1,080
Weighted-average shares outstanding — diluted	36,914	36,305
Net income per share — basic	$ 0.18us-gaap_EarningsPerShareBasic	$ 0.18us-gaap_EarningsPerShareBasic
Net income per share — diluted	$ 0.17us-gaap_EarningsPerShareDiluted	$ 0.17us-gaap_EarningsPerShareDiluted
Anti-dilutive weighted-average shares related to stock award plans (in shares)	484	347

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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