Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents	$ 16,528	$ 14,528
Marketable securities	207,603	115,608
Accounts receivable	1,142	8,616
Prepaid expenses and other current assets	5,606	2,901
Total current assets	230,879	141,653
Property and equipment, net	7,088	3,105
Patents, licenses, and other intangible assets, net	11,148	10,362
Marketable securities - long term	139,198	273,340
Income tax receivable	1,524
Other assets	265	103
Total assets	390,102	428,563
Current liabilities
Accounts payable	6,869	3,880
Accrued expenses	5,480	6,692
Current portion of deferred rent	26	128
Current portion of deferred revenue	88,813	95,521
Income tax payable	157	65
Total current liabilities	101,345	106,286
Deferred rent, less current portion	1,088	397
Deferred revenue, less current portion	5,623	7,926
Total liabilities	108,056	114,609
Commitments and contingencies (see note 8)
Stockholders' equity
Preferred stock, $0.01 par value: 10,000,000 authorized shares; -0- issued and outstanding shares at December 31, 2017 and 2016
Common stock, $0.01 par value: 200,000,000 authorized shares; 47,002,488 issued and outstanding shares at December 31, 2017 and 46,567,978 issued and outstanding at December 31, 2016	470	466
Additional paid-in capital	570,670	552,889
Accumulated other comprehensive loss	(1,808)	(1,441)
Accumulated deficit	(287,286)	(237,960)
Total stockholders' equity	282,046	313,954
Total liabilities and stockholders' equity	$ 390,102	$ 428,563

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).

Name:	us-gaap_AccountsPayableCurrent
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.