CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 67,753	$ 84,783
Available-for-sale securities	192,477	184,736
Accounts receivable, net	11,443	9,478
Inventories	17,190	16,186
Prepaid expenses and other assets	4,505	8,251
Total current assets	293,368	303,434
Property and equipment, net	738	788
Non-current assets	1,379	1,554
Total assets	295,485	305,776
Current liabilities:
Accounts payable	4,907	4,707
Accrued and other liabilities	20,313	15,686
Deferred revenue	1,505	19,174
Current portion of long-term debt	9,311	8,708
Total current liabilities	36,036	48,275
Long-term debt, net of current portion	234,866	232,610
Deferred revenue, net of current portion	6,232	6,449
Non-current accrued and other liabilities	370	257
Total liabilities	277,504	287,591
Commitments and contingencies
Stockholders' equity
Preferred stock; $1.00 par value; 5,000 shares authorized; no shares issued and outstanding at March 31, 2017 and December 31, 2016
Common stock; $.001 par value; 200,000 shares authorized; 105,629 and 104,874 shares issued and outstanding at March 31, 2017 and December 31, 2016, respectively	105	105
Additional paid-in capital	832,477	831,750
Accumulated other comprehensive loss	(491)	(616)
Accumulated deficit	(814,110)	(813,054)
Total stockholders' equity	17,981	18,185
Total liabilities and stockholders' equity	$ 295,485	$ 305,776