Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash flows from operating activities
Net loss	$ (14,635)	$ (6,398)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	410	282
Amortization of premium on marketable securities	659	426
Stock-based compensation	3,158	1,960
Abandonment of capitalized intangible assets	9	9
Gain on sale of marketable securities available-for-sale		(3)
Changes in operating assets and liabilities:
Accounts receivable	1,678	(604)
Interest receivable	(479)	41
Prepaid expenses and other assets	(1,465)	(683)
Accounts payable	395	(2,109)
Accrued expenses	(190)	(1,243)
Income taxes	110
Deferred rent	(30)	(26)
Deferred revenue	(340)	(5,952)
Net cash used in operating activities	(10,720)	(14,300)
Cash flows from investing activities
Purchase of marketable securities	(6,988)	(16,340)
Purchase of intangible assets	(702)	(343)
Purchase of property and equipment	(494)	(317)
Proceeds from sale and maturities of marketable securities	16,911	26,660
Net cash provided by investing activities	8,727	9,660
Cash flows from financing activities
Proceeds from issuance of common stock upon exercise of stock awards	1,026	200
Net cash provided by financing activities	1,026	200
Net decrease in cash and cash equivalents	(967)	(4,440)
Cash and cash equivalents, beginning of period	14,528	12,590
Cash and cash equivalents, end of period	13,561	8,150
Cash paid during the period for:
Interest	3
Income taxes	60
Supplemental disclosures of non-cash investing activities
Unrealized gain on marketable securities available for sale	$ 245	$ 619