Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 25,273	$ 29,798
Short-term investments	89,432	96,675
Prepaid expenses and other current assets	1,928	1,876
Total current assets	116,633	128,349
Property and equipment, net	1,122	1,130
Other assets	168	168
Total assets	117,923	129,647
Current liabilities:
Accounts payable	1,902	1,592
Accrued expenses and other current liabilities	2,886	4,416
Accrued interest	480	1,204
Total current liabilities	5,268	7,212
Other long-term liabilities	292	307
Total liabilities	54,659	56,479
Commitments and Contingencies (Note 7)
Stockholders’ equity:
Preferred Stock, $0.001 par value: 5,000,000 shares authorized and no shares issued or outstanding
Common stock, $0.01 par value: 120,000,000 shares authorized at March 31, 2017 and December 31, 2016; 26,986,318 shares issued and outstanding at March 31, 2017 and December 31, 2016	270	270
Additional paid-in capital	312,613	311,829
Accumulated deficit	(249,547)	(238,877)
Accumulated other comprehensive loss	(72)	(54)
Total stockholders’ equity	63,264	73,168
Total liabilities and stockholders’ equity	117,923	129,647
2021 Convertible Notes [Member]
Current liabilities:
2021 Convertible Notes, net of issuance costs	$ 49,099	$ 48,960