Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Operating activities
Net loss	$ (3,545)	$ (12,451)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization	5,434	4,365
Employee stock-based compensation	10,302	9,389
Impairment of assets held for sale and long-lived assets		56
Gain on disposal of property and equipment	35
Outside director restricted stock awarded in lieu of fees	100	100
Gain on sale of equity securities	(2,807)	(2,009)
Deferred tax benefit from unrealized gain on available-for-sale marketable securities, net	820	348
Changes in assets and liabilities:
Accounts receivable	2,752	3,553
Prepaid expenses and other assets	1,384	(1,186)
Accounts payable	2,161	(2,368)
Accrued compensation and employee benefits	(6,545)	(1,725)
Accrued expenses and other liabilities	1,795	3,970
Deferred revenues		(197)
Net cash provided by operating activities	11,886	1,845
Investing activities
Purchases of property and equipment	(8,057)	(6,879)
Proceeds from sale of property and equipment	10
Purchases of marketable securities	(50,338)	(35,932)
Maturities of marketable securities	29,932	40,007
Proceeds from sales of marketable securities	10,155	5,117
Net cash (used in) provided by investing activities	(18,298)	2,313
Financing activities
Net proceeds from issuance of common stock under stock plans	12,522	7,072
Withholding taxes related to restricted stock units net share settlement	(4,314)	(3,103)
Net cash provided by financing activities	8,208	3,969
Net increase in cash and cash equivalents	1,796	8,127
Cash and cash equivalents at the beginning of the period	40,404	32,533
Cash and cash equivalents at the end of the period	42,200	40,660
Non-cash investing and financing activities
Accrued purchases of property and equipment	$ 2,005	605
Change in fair value of equity investment		$ (1,404)