Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 64,833	$ 111,355
Investments	192,950	94,375
Prepaid expenses and other assets	5,846	3,358
Total current assets	263,629	209,088
Property and equipment, net	9,844	2,027
Goodwill	30,815	30,815
Restricted cash	1,525	1,436
Deposits	455	545
Operating lease right-of-use assets	2,452	0
Investments	0	7,402
Total assets	308,720	251,313
Current liabilities:
Accounts payable and accrued expenses	14,168	15,372
Operating lease liabilities, current	913	0
Total current liabilities	15,081	15,372
Convertible notes, net of unamortized discount	43,180	41,447
Operating lease liabilities, non-current	1,933	0
Other liabilities	22	457
Total liabilities	60,216	57,276
Commitments and contingencies (Note 11)
Stockholders' equity:
Common stock, $0.01 par value, 120,000,000 shares authorized; 50,332,435 and 45,194,736 shares issued and outstanding at June 30, 2019 and December 31, 2018, respectively	503	452
Treasury stock, at cost, 22,308 and 50,000 common shares at June 30, 2019 and December 31, 2018, respectively	(344)	(668)
Additional paid-in capital	392,205	300,253
Accumulated other comprehensive income (loss)	144	(127)
Accumulated deficit	(144,004)	(105,873)
Total stockholders' equity	248,504	194,037
Total liabilities and stockholders' equity	308,720	251,313
Series A Convertible Preferred Shares [Member]
Stockholders' equity:
Preferred shares	0	0
Series B Convertible Preferred Shares [Member]
Stockholders' equity:
Preferred shares	$ 0	$ 0