Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 147,304	$ 127,789
Marketable securities	224,338	264,589
Accounts receivable, net	2,397	410
Inventories	2,525	1,799
Prepaid expenses and other current assets	4,023	3,403
Total current assets	380,587	397,990
Property and equipment, net	10,964	11,189
Long-term investments	4,938	31,538
Restricted cash	600	600
Total assets	397,089	441,317
Current liabilities:
Accounts payable	3,420	6,222
Accrued expenses and other current liabilities	11,060	14,383
Current portion of long-term debt	9,967	9,967
Total current liabilities	24,447	30,572
Long-term debt, net	10,612	12,936
2024 convertible notes, net	138,983	137,107
Other long-term liabilities	440	428
Total liabilities	174,482	181,043
Commitments and contingencies
Preferred stock, $0.001 par value; 10,000,000 shares authorized at March 31, 2018 and December 31, 2017 and 0 shares issued and outstanding at March 31, 2018 and December 31, 2017	0	0
Stockholders’ equity:
Common stock, $0.001 par value; 100,000,000 shares authorized; 37,632,589 and 37,610,897 shares issued and outstanding, at March 31, 2018 and December 31, 2017, respectively	38	38
Additional paid-in capital	613,881	609,810
Accumulated other comprehensive loss	(576)	(407)
Accumulated deficit	(390,736)	(349,167)
Total stockholders’ equity	222,607	260,274
Total liabilities and stockholders’ equity	$ 397,089	$ 441,317