Condensed Consolidated Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Current Assets
Cash and cash equivalents	$ 230,261	$ 170,566
Prepaid expenses and other current assets	4,186	2,398
Total current assets	234,447us-gaap_AssetsCurrent	172,964us-gaap_AssetsCurrent
Other assets	284us-gaap_OtherAssetsNoncurrent	616us-gaap_OtherAssetsNoncurrent
Property and equipment, net	664us-gaap_PropertyPlantAndEquipmentNet	714us-gaap_PropertyPlantAndEquipmentNet
Total assets	235,395us-gaap_Assets	174,294us-gaap_Assets
Current liabilities
Accounts Payable	601us-gaap_AccountsPayableCurrent	1,259us-gaap_AccountsPayableCurrent
Accrued liabilities	7,219us-gaap_AccruedLiabilitiesCurrent	5,666us-gaap_AccruedLiabilitiesCurrent
Total Current Liabilities	7,820us-gaap_LiabilitiesCurrent	6,925us-gaap_LiabilitiesCurrent
Total Liabilities	7,820us-gaap_Liabilities	6,925us-gaap_Liabilities
Commitments and contingencies (Note 6)
Stockholders' equity
Preferred stock, $0.0001 par value; 5,000,000 shares authorized at March 31, 2015 and December 31, 2014, respectively; zero shares issued and outstanding at March 31, 2015 and December 31, 2014, respectively
Common stock, $0.0001 par value, 50,000,000 shares authorized at March 31, 2015 and December 31, 2014; 29,257,836 and 24,245,437 shares issued and outstanding at March 31, 2015 and December 31, 2014, respectively	3us-gaap_CommonStockValue	2us-gaap_CommonStockValue
Additional paid-in capital	360,838us-gaap_AdditionalPaidInCapital	278,626us-gaap_AdditionalPaidInCapital
Accumulated deficit	(133,266)	(111,259)
Total stockholders' equity	227,575us-gaap_StockholdersEquity	167,369us-gaap_StockholdersEquity
Total liabilities and stockholders’ equity	$ 235,395	$ 174,294

Carrying value as of the balance sheet date of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19

-Subparagraph a

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(a))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682