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Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	Nov. 30, 2015	Dec. 10, 2013
Earnings Per Share, Basic and Diluted [Abstract]
Net loss	$ (15,245)	$ (10,917)	$ (129,752)	$ (35,131)
Shares used in computing basic and diluted net loss per share (in shares)	82,446	67,810	80,402	67,568
Basic and diluted net loss per share (in dollars per share)	$ (0.18)	$ (0.16)	$ (1.61)	$ (0.52)
Securities Excluded from Calculations of Earnings Per Share Because Impact Would Have Been Anti-Dilutive [Abstract]
Outstanding securities used in calculations (in shares)	2,609	1,942	1,875	2,119
Convertible notes	$ 174,734		$ 174,734		$ 167,748
Potential Dilutive Effect of Securities [Abstract]
Conversion of the Notes (in shares)	14,767	3,588	14,767	3,588
Convertible Debt \| 2.25% Convertible Senior Notes
Securities Excluded from Calculations of Earnings Per Share Because Impact Would Have Been Anti-Dilutive [Abstract]
Convertible notes	$ 76,800		$ 76,800				$ 86,300
Stated interest rate	2.25%		2.25%
Convertible Debt \| 3.25% Convertible Senior Notes
Securities Excluded from Calculations of Earnings Per Share Because Impact Would Have Been Anti-Dilutive [Abstract]
Convertible notes	$ 101,900		$ 101,900			$ 125,000
Stated interest rate	3.25%		3.25%
Common stock options
Securities Excluded from Calculations of Earnings Per Share Because Impact Would Have Been Anti-Dilutive [Abstract]
Outstanding securities used in calculations (in shares)	2,006	1,600	1,384	1,739
Restricted stock awards
Securities Excluded from Calculations of Earnings Per Share Because Impact Would Have Been Anti-Dilutive [Abstract]
Outstanding securities used in calculations (in shares)	138	135	133	133
Restricted stock units
Securities Excluded from Calculations of Earnings Per Share Because Impact Would Have Been Anti-Dilutive [Abstract]
Outstanding securities used in calculations (in shares)	465	207	358	247