Consolidated Statements of Comprehensive Loss (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Net loss	$ (50,038)us-gaap_NetIncomeLoss	$ (29,281)us-gaap_NetIncomeLoss	$ (17,708)us-gaap_NetIncomeLoss
Other comprehensive loss:
Unrealized gain (loss) on short-term investments	(65)	22	0
Comprehensive loss	$ (50,103)us-gaap_ComprehensiveIncomeNetOfTax	$ (29,259)us-gaap_ComprehensiveIncomeNetOfTax	$ (17,708)us-gaap_ComprehensiveIncomeNetOfTax

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

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