Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets
Cash and cash equivalents	$ 69,418	$ 163,620
Investment securities, available-for-sale	271,924	365,416
Accounts receivable, net	17,343	5,903
Interest and other receivables	1,087	1,237
Inventory	5,248	4,175
Prepaid expenses	8,457	7,546
Total current assets	373,477	547,897
Property and equipment, net	2,662	3,081
Intangible assets, net	5,538	7,015
Restricted cash	2,475	2,375
Other assets	354	785
Total assets	384,506	561,153
Liabilities and stockholders’ equity
Accounts payable	8,786	3,912
Accrued liabilities	40,244	36,029
Deferred revenue		2,644
Total current liabilities	49,030	42,585
Long-term liabilities	191	157
Total liabilities	49,221	42,742
Commitments and contingencies (Note 9)
Stockholders’ equity:
Preferred stock, $0.0001 par value; 5,000,000 shares authorized at December 31, 2017 and 2016; no shares issued and outstanding at December 31, 2017 and 2016
Common stock, $0.0001 par value; 225,000,000 shares authorized at December 31, 2017 and December 31, 2016; 124,410,552 shares and 121,367,169 shares issued and outstanding at December 31, 2017 and December 31, 2016, respectively	12	12
Additional paid-in capital	1,559,343	1,452,272
Accumulated deficit	(1,223,671)	(933,979)
Accumulated other comprehensive (loss) income	(399)	106
Total stockholders’ equity	335,285	518,411
Total liabilities and stockholders’ equity	$ 384,506	$ 561,153

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).

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.