CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows provided by (used in) operating activities:
Net income (loss)	$ 54,343	$ (45,291)	$ (39,381)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation and amortization of property and equipment	855	968	910
Stock-based compensation	8,686	6,102	6,111
Deferred income taxes	109	(32)	24,274
Loss on disposal of equipment	26	1	19
Income from discontinued operations	0	0	(649)
Changes in operating assets and liabilities:
Accounts and other receivables	(245)	576	(171)
Prepaid income taxes	0	0	1,998
Prepaid expenses and other current assets	(4,015)	141	(86)
Other assets	(7,188)	(197)	(275)
Accounts payable	(3,035)	696	5,322
Accrued compensation and other current liabilities	(887)	(1,111)	967
Deferred revenue	21,406	(5,575)	23,090
Other long-term liabilities	(131)	(107)	(87)
Net cash provided by (used in) operating activities	69,924	(43,829)	22,042
Cash flows provided by investing activities:
Purchases of short-term investments	(17,693)	(23,807)	(32,813)
Proceeds from maturities of short-term investments	26,004	35,000	40,000
Purchases of property and equipment	(74)	(125)	(343)
Proceeds from discontinued operations	0	0	1,000
Net cash provided by investing activities	8,237	11,068	7,844
Cash flows provided by financing activities:
Issuance of common stock under employee stock purchase plan	218	328	307
Exercise of stock options, net of shares withheld for employee taxes	7,987	518	2,388
Purchases of treasury stock	0	(328)	(729)
Net cash provided by financing activities	8,205	518	1,966
Net increase (decrease) in cash and cash equivalents	86,366	(32,243)	31,852
Cash and cash equivalents:
Beginning of year	24,622	56,865	25,013
End of year	110,988	24,622	56,865
Supplemental disclosure of cash flow information:
Cash paid for taxes	151	191	(419)
Supplemental disclosure of noncash operating, investing, and financing activities:
Amounts accrued for property and equipment	0	0	22
Cashless option exercise under company stock plan	1,478	0	177
Release of Restricted Stock Units and Awards under company stock plan	$ 2,806	$ 2,661	$ 2,257