Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 7,559	$ 2,013
Short-term investments	40,966	48,547
Accounts receivable	284	349
Unbilled revenue	112	184
Inventories — current	242	252
Prepaid expenses and other current assets	1,281	877
Total current assets	50,444	52,222
Property and equipment, net	486	508
Inventories — noncurrent	1,276	1,327
Long-term investments		2,498
Other noncurrent assets	442	19
Total assets	52,648	56,574
Current liabilities:
Accounts payable and accrued expenses	2,183	2,359
Amounts due to related parties	20	30
Notes payable — current	2,083	0
Unearned revenue — current	885	740
Total current liabilities	5,171	3,129
Notes payable — noncurrent	23,092	25,127
Unearned revenue — noncurrent	3,014	3,120
Other noncurrent liabilities	3,000	3,000
Total liabilities	34,277	34,376
Stockholders’ equity:
Common stock, $0.001 par value—400,000,000 shares authorized as of March 31, 2017 and December 31, 2016; 42,664,821 and 44,487,678 shares issued and outstanding as of March 31, 2017 and December 31, 2016	43	44
Additional paid-in capital	174,114	173,723
Accumulated deficit	(155,766)	(151,550)
Accumulated other comprehensive loss	(20)	(19)
Total stockholders’ equity	18,371	22,198
Total liabilities and stockholders’ equity	$ 52,648	$ 56,574