Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities:
Net income	$ 2,858	$ 4,123	$ 40,155
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization of property and equipment	996	500	584
Amortization of intangibles	20	67	79
Stock-based compensation	5,470	5,295	4,644
Allowance for doubtful accounts	(6)	16	8
Loss on disposal of equipment	10	52	11
Changes in operating assets and liabilities:
Accounts and other receivables	1,814	(2,439)	1,272
Inventories	0	0	141
Deferred income taxes	9,935	1,893	(36,850)
Prepaid income taxes	(6,995)	0	0
Prepaid expenses and other current assets	(1,945)	(155)	16
Other assets	(36)	(39)	(152)
Accounts payable	(19)	(10)	341
Accrued compensation and other current liabilities	3,750	(2,241)	2,788
Deferred revenue	(6,394)	(6,755)	8,206
Other long-term liabilities	587	(16)	(91)
Net cash provided by operating activities	10,045	291	21,152
Cash flows provided by (used in) investing activities:
Purchases of short-term investments	(44,910)	(42,953)	(94,931)
Proceeds from maturities of short-term investments	48,000	57,000	77,000
Purchases of property and equipment	(4,430)	(779)	(234)
Net cash provided by (used in) investing activities	(1,340)	13,268	(18,165)
Cash flows provided by (used in) financing activities:
Issuance of common stock under employee stock purchase plan	367	381	198
Exercise of stock options	1,561	1,304	6,393
Purchases of treasury stock	0	(15,000)	0
Net cash provided by (used in) financing activities	1,928	(13,315)	6,591
Net increase in cash and cash equivalents	10,633	244	9,578
Cash and cash equivalents:
Beginning of year	14,380	14,136	4,558
End of year	25,013	14,380	14,136
Supplemental disclosure of cash flow information:
Cash paid for taxes	156	47	18
Supplemental disclosure of noncash operating, investing, and financing activities:
Amounts accrued for property and equipment	18	60	24
Cashless option exercise under company stock plan	69	0	0
Release of Restricted Stock Units and Awards under company stock plan	$ 3,059	$ 3,976	$ 3,482