CONSOLIDATED STATEMENTS OF CASH FLOW - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net loss	$ (20,436)	$ (33,261)
Adjustments to reconcile net loss to net cash used for operating activities:
Depreciation and amortization	656	823
Amortization of debt issuance costs and discounts	15,163	13,860
Amortization of discount or premium on available-for-sale securities	605	700
Share-based compensation expense	2,221	1,740
Changes in assets and liabilities:
Accounts receivable	(2,328)	(1,298)
Inventories	2,744	2,343
Prepaid expenses and other assets	4,490	4,206
Accounts payable	(277)	(620)
Accrued and other liabilities	4,211	(7,227)
Deferred revenue	(18,534)	67,323
Net cash used for operating activities	(11,485)	48,589
Cash flows from investing activities:
Property and equipment purchases	(21)
Purchases of available-for-sale securities	(20,915)	(50,523)
Proceeds from maturity of available-for-sale securities	29,120	60,050
Proceeds from sales of available-for-sale securities	13,413	6,960
Net cash (used for) provided by investing activities	21,597	16,487
Cash flows from financing activities:
Repayments of notes payable	(21,770)	(6,359)
Sale of common stock through employee stock purchase plan	26	25
Net cash used for financing activities	(21,744)	(6,334)
Net (decrease) increase in cash and cash equivalents	(11,632)	58,742
Cash and cash equivalents:
Beginning of period	84,783	95,395
End of period	$ 73,151	$ 154,137