CONSOLIDATED STATEMENTS OF CASH FLOW - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash flows from operating activities:
Net loss	$ (14,442)	$ (24,109)
Adjustments to reconcile net loss to net cash used for operating activities:
Depreciation and amortization	501	564
Amortization of debt issuance costs and discounts	9,973	9,143
Amortization of discount or premium on available-for-sale securities	442	503
Share-based compensation expense	1,468	1,099
Changes in assets and liabilities:
Accounts receivable	1,037	(2,045)
Inventories	558	2,793
Prepaid expenses and other assets	2,912	2,523
Accounts payable	(323)	1,140
Accrued and other liabilities	4,783	(7,052)
Deferred revenue	(18,197)	(1,894)
Net cash used for operating activities	(11,288)	(17,335)
Cash flows from investing activities:
Property and equipment purchases	(21)
Purchases of available-for-sale securities	(20,915)	(32,523)
Proceeds from maturity of available-for-sale securities	23,120	37,450
Proceeds from sales of available-for-sale securities	7,208	3,703
Net cash provided by investing activities	9,392	8,630
Cash flows from financing activities:
Repayments of notes payable	(6,507)	(4,169)
Sale of common stock through employee stock purchase plan	26	24
Net cash used for financing activities	(6,481)	(4,145)
Net decrease in cash and cash equivalents	(8,377)	(12,850)
Cash and cash equivalents:
Beginning of period	84,783	95,395
End of period	$ 76,406	$ 82,545