CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows provided by (used in) operating activities:
Net income (loss)	$ 57,485	$ (32,997)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation and amortization of property and equipment	647	709
Stock-based compensation	6,266	4,073
Deferred income taxes	67	(75)
Loss on disposal of equipment	26	1
Changes in operating assets and liabilities:
Accounts and other receivables	(454)	(5,096)
Prepaid expenses and other current assets	(1,870)	(101)
Other assets	(3,910)	(146)
Accounts payable	(5,889)	(1,116)
Accrued compensation and other current liabilities	466	(3,209)
Income tax payable	(219)	0
Deferred revenue	22,713	(4,082)
Other long-term liabilities	211	(78)
Net cash provided by (used in) operating activities	75,539	(42,117)
Cash flows provided by investing activities:
Purchases of short-term investments	(17,693)	(23,807)
Proceeds from maturities of short-term investments	22,000	28,000
Purchases of property and equipment	(63)	(121)
Net cash provided by investing activities	4,244	4,072
Cash flows provided by financing activities:
Issuance of common stock under employee stock purchase plan	218	328
Exercise of stock options	8,010	443
Purchases of treasury stock	0	328
Net cash provided by financing activities	8,228	443
Net increase (decrease) in cash and cash equivalents	88,011	(37,602)
Cash and cash equivalents:
Beginning of period	24,622	56,865
End of period	112,633	19,263
Supplemental disclosure of cash flow information:
Cash paid for taxes	139	128
Supplemental disclosure of noncash operating, investing, and financing activities:
Amounts accrued for treasury stocks	569	0
Release of Restricted Stock Units and Awards under company stock plan	$ 2,806	$ 2,524