Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating activities
Net loss	$ (9,417)	$ (5,996)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation of property and equipment	111	98
Stock-based compensation	2,541	2,399
Noncash interest (income) expense, net	(366)	44
Changes in assets and liabilities:
Accounts receivable	49,392	30,205
Prepaids and other current assets	(83)	(685)
Other assets	32	(51)
Accounts payable	(951)	148
Other liabilities	(1,372)	(1,851)
Deferred revenue	1,061	1,769
Net cash provided by operating activities	40,948	26,080
Investing activities
Purchases of property and equipment, net	(32)	(177)
Purchases of investments	(77,941)	(55,387)
Maturities of investments	26,900	36,350
Net cash used in investing activities	(51,073)	(19,214)
Financing activities
Proceeds from exercise of stock options	1,128	361
Employees' tax withheld and paid for restricted stock units	(473)	(297)
Net cash provided by financing activities	655	64
Net increase (decrease) in cash and cash equivalents	(9,470)	6,930
Cash and cash equivalents at beginning of period	40,020	12,024
Cash and cash equivalents at end of period	$ 30,550	$ 18,954