Consolidated Statements of Stockholders' (Deficit) Equity - USD ($) $ in Thousands	Total	Termination of ADM Operating Agreement	Common Stock	Additional Paid-In Capital	Additional Paid-In Capital Vesting of Warrants [Member]	Additional Paid-In Capital Termination of ADM Operating Agreement	Accumulated Other Comprehensive Loss	Accumulated Deficit
Common stock, shares outstanding, beginning at Dec. 31, 2012	61,000,724
Beginning Balance at Dec. 31, 2012	$ 183,311		$ 61	$ 373,577			$ (399)	$ (189,928)
Issuance of common stock under stock plans, net of shares used for tax withholdings (in shares)			1,347,617
Issuance of common stock under stock plans, net of shares used for tax withholdings	5,326		$ 1	5,325
Common stock issued pursuant to vesting of restricted stock and restricted stock units (in shares)			83,835
Common stock issued pursuant to vesting of restricted stock and restricted stock units	5,209			5,209
Stock-based compensation expense	13,444			13,444
Common stock issued upon early conversion of senior convertible notes (in shares)			5,541,597
Common stock issued upon early conversion of senior convertible notes	44,218		$ 6	44,212
Common stock issued			770,761
Common stock issued during period, Other	7,126		$ 1	7,125
Vesting of warrants	98				$ 98
Change in unrealized gain/loss on available-for-sale securities	(240)						(240)
Foreign currency translation adjustment	(3,155)						(3,155)
Net loss	(116,389)							(116,389)
Ending Balance at Dec. 31, 2013	$ 138,948		$ 69	448,990			(3,794)	(306,317)
Common stock, shares outstanding, beginning at Dec. 31, 2013	68,744,534
Issuance of common stock under stock plans, net of shares used for tax withholdings (in shares)			1,367,075
Issuance of common stock under stock plans, net of shares used for tax withholdings	$ 8,880		$ 1	8,879
Issuance of common stock pursuant to secondary offering (in shares)			5,750,000
Issuance of common stock pursuant to secondary offering	59,209		$ 6	59,203
Common stock issued pursuant to vesting of restricted stock and restricted stock units (in shares)			782,985
Common stock issued pursuant to vesting of restricted stock and restricted stock units	8,518		$ 1	8,517
Stock-based compensation expense	17,032			17,032
Common stock issued upon early conversion of senior convertible notes (in shares)			2,743,475
Common stock issued upon early conversion of senior convertible notes	22,594		$ 2	22,592
Common stock issued during period, Other	0
Vesting of warrants	556				556
Change in unrealized gain/loss on available-for-sale securities	(312)						(312)
Foreign currency translation adjustment	(6,908)						(6,908)
Net loss	(162,141)							(162,141)
Ending Balance at Dec. 31, 2014	$ 86,376		$ 79	565,769			(11,014)	(468,458)
Common stock, shares outstanding, beginning at Dec. 31, 2014	79,388,069
Issuance of common stock under stock plans, net of shares used for tax withholdings (in shares)			416,008
Issuance of common stock under stock plans, net of shares used for tax withholdings	$ 837		$ 1	836
Common stock issued pursuant to vesting of restricted stock and restricted stock units (in shares)			808,087
Common stock issued pursuant to vesting of restricted stock and restricted stock units	5,633		$ 1	5,632
Stock-based compensation expense	10,052			10,052
Common stock issued			1,121,914
Common stock issued during period, Other	3,052		$ 1	3,051
Vesting of warrants	97	$ 242			$ 97	$ 242
Change in unrealized gain/loss on available-for-sale securities	228						228
Foreign currency translation adjustment	(11,545)						(11,545)
Net loss	(141,447)							(141,447)
Ending Balance at Dec. 31, 2015	$ (46,475)		$ 82	$ 585,679			$ (22,331)	$ (609,905)