Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 53,847	$ 45,518
Short-term marketable securities	99,098	84,057
Accounts receivable (net of allowance for doubtful accounts; 2018—$2,184, 2017—$3,884)	48,982	31,161
Prepaid expenses and other current assets	13,449	13,524
Total current assets	215,376	174,260
Property and equipment, net	40,054	46,440
Other assets	13,586	10,917
Total assets	269,016	231,617
Current liabilities:
Accounts payable	5,192	156
Accrued compensation and employee benefits	21,750	24,953
Accrued expenses and other current liabilities	12,705	14,084
Other current liabilities	340	323
Total current liabilities	39,987	39,516
Other liabilities	3,826	3,810
Commitments and contingencies
Stockholders' equity:
Common stock	3	3
Additional paid-in capital	482,835	464,637
Accumulated other comprehensive loss	(65)	(294)
Accumulated deficit	(227,460)	(245,945)
Treasury stock, at cost	(30,110)	(30,110)
Total stockholders' equity	225,203	188,291
Total liabilities and stockholders' equity	$ 269,016	$ 231,617

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.