Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 249,501	$ 197,569
Short-term investments	84,476	52,086
Inventory	1,062	0
Prepaid expenses and other current assets	6,115	4,487
Total current assets	341,154	254,142
Property, plant and equipment, net	47,810	31,932
Other assets	2,079	4,202
Total assets	391,043	290,276
Current liabilities
Accounts payable	6,066	6,245
Accrued expenses and other current liabilities	19,070	18,939
Total current liabilities	25,136	25,184
Convertible notes, net	123,922	123,845
Other non-current liabilities	5,714	5,648
Total liabilities	154,772	154,677
Commitments and contingencies (Note 10)
Stockholders’ equity
Preferred stock, $0.001 par value; 15,000,000 shares authorized as of March 31, 2018 and December 31, 2017; None issued and outstanding	0	0
Common stock, $0.001 par value; 150,000,000 shares authorized as of March 31, 2018 and December 31, 2017; 39,503,110 and 36,947,637 shares issued and outstanding as of March 31, 2018 and December 31, 2017, respectively	40	37
Additional paid-in capital	740,952	597,318
Accumulated other comprehensive loss	(157)	(28)
Accumulated deficit	(504,564)	(461,728)
Total stockholders’ equity	236,271	135,599
Total liabilities and stockholders’ equity	$ 391,043	$ 290,276