CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows provided by (used in) operating activities:
Net income (loss)	$ (19,636)	$ 62,125
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation and amortization	405	439
Stock-based compensation	3,184	3,752
Deferred income taxes	60	66
Other	0	26
Changes in operating assets and liabilities:
Accounts and other receivables	(3,916)	(220)
Prepaid expenses and other current assets	1,539	(215)
Other assets	(11,175)	(4,077)
Accounts payable	3,762	(3,288)
Accrued compensation	(2,003)	(953)
Other current liabilities	1,742	150
Deferred revenue	(2,108)	23,917
Other long-term liabilities	4,231	239
Net cash provided by (used in) operating activities	(23,915)	81,961
Cash flows provided by (used in) investing activities:
Purchases of short-term investments	(8,930)	(17,693)
Proceeds from maturities of short-term investments	14,000	19,500
Purchases of property and equipment	(9)	(31)
Net cash provided by investing activities	5,061	1,776
Cash flows provided by financing activities:
Proceeds from issuance of common stock under employee stock purchase plan	109	98
Proceeds from stock options exercises	371	7,980
Net cash provided by financing activities	480	8,078
Net increase (decrease) in cash and cash equivalents	(18,374)	91,815
Cash and cash equivalents:
Beginning of period	110,988	24,622
End of period	92,614	116,437
Supplemental disclosure of cash flow information:
Cash paid for income taxes	25	81
Supplemental disclosure of noncash operating, investing, and financing activities:
Release of restricted stock units and awards under company stock plan	$ 7,065	$ 2,546