Consolidated Statements of Stockholders' Equity - 6 months ended Jun. 30, 2017 - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Equity (Deficit) [Member]
Beginning Balance, Amount at Dec. 31, 2016	$ 118,700	$ 36	$ 365,444	$ (864)	$ (245,916)
Beginning Balance, Shares at Dec. 31, 2016		35,784
Issuance of common stock under stock plans, net of shares withheld for employee taxes	5,156		5,156
Issuance of common stock under stock plans, net of shares withheld for employee taxes, Shares		977
Stock-based compensation	23,132		23,132
Cumulative adjustment from adoption of stock compensation standard			452		(452)
Cumulative translation adjustment	564			564
Unrealized gain on investments, net of income taxes of $20	34			34
Equity component of 2022 Notes (Note 6)	73,713		73,713
Net loss	(17,596)				(17,596)
Ending Balance, Amount at Jun. 30, 2017	$ 203,703	$ 36	$ 467,897	$ (266)	$ (263,964)
Ending Balance, Shares at Jun. 30, 2017		36,761