Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 258,567	$ 159,678
Restricted cash	47	0
Marketable securities	73,880	313,661
Prepaid expenses and other current assets	2,315	6,969
Total current assets	334,809	480,308
Property and equipment, net	4,922	1,897
Other assets	551	260
Total assets	340,282	482,465
Current liabilities:
Accounts payable	6,128	6,228
Accrued expenses and other current liabilities	26,597	14,952
Total current liabilities	32,725	21,180
Other non-current liabilities	379	0
Total liabilities	33,104	21,180
Commitments and contingencies
Stockholders' equity:
Common stock, $.0001 par value; 200,000,000 shares authorized, 43,141,134 shares and 42,984,243 shares issued and outstanding at December 31, 2016 and 2015, respectively	4	4
Additional paid-in-capital	935,671	907,040
Accumulated other comprehensive income	71	5
Accumulated deficit	(628,568)	(445,764)
Total stockholders' equity	307,178	461,285
Total liabilities and stockholders' equity	$ 340,282	$ 482,465

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

Carrying value as of the balance sheet date of obligations incurred and payable, pertaining to costs that are statutory in nature, are incurred on contractual obligations, or accumulate over time and for which invoices have not yet been received or will not be rendered. Examples include taxes, interest, rent and utilities. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).