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Net Loss Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 10, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net loss	$ (14,782)us-gaap_NetIncomeLoss	$ (13,938)us-gaap_NetIncomeLoss	$ (8,993)us-gaap_NetIncomeLoss	$ 5,295us-gaap_NetIncomeLoss	$ (3,412)us-gaap_NetIncomeLoss	$ (8,990)us-gaap_NetIncomeLoss	$ 5,670us-gaap_NetIncomeLoss	$ (9,335)us-gaap_NetIncomeLoss	$ (32,418)us-gaap_NetIncomeLoss	$ (16,068)us-gaap_NetIncomeLoss	$ (35,774)us-gaap_NetIncomeLoss
Shares used in computing basic and diluted net loss per share									65,225	62,607	59,811
Basic and diluted net loss per share (in USD per share)									$ (0.50)us-gaap_EarningsPerShareBasicAndDiluted	$ (0.26)us-gaap_EarningsPerShareBasicAndDiluted	$ (0.60)us-gaap_EarningsPerShareBasicAndDiluted
Securities excluded from calculations of net loss per share because impact would have been anti-dilutive									2,325	3,011	3,595
Convertible notes	70,407us-gaap_ConvertibleNotesPayable				67,101us-gaap_ConvertibleNotesPayable				70,407us-gaap_ConvertibleNotesPayable	67,101us-gaap_ConvertibleNotesPayable
Incremental Common Shares Attributable to Conversion of Debt Securities									3,588	3,588	0
Employee Stock Option
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculations of net loss per share because impact would have been anti-dilutive									1,822	2,374	2,698
Restricted Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculations of net loss per share because impact would have been anti-dilutive									321	403	405
Restricted Stock Units (RSUs)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculations of net loss per share because impact would have been anti-dilutive									182	234	492
Convertible Senior Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Convertible notes												$ 86,300
Debt Instrument, Interest Rate, Stated Percentage												2.25%