Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Schedule of reconciliation of income taxes computed using the U.S. federal statutory rate to that reflected in operations

A reconciliation of income taxes computed using the U.S. federal statutory rate to that reflected in operations follows (in thousands):

	Year Ended December 31,
	2017			2016			2015
Income tax benefit using U.S. federal statutory rate	$	(86,426	)	$	(62,141	)	$	(34,391	)
State income taxes, net of federal benefit	(22,148		)	(5,236		)	(4,434		)
Stock-based compensation	(5,909		)	1,585			752
Research and development tax credits	(2,468		)	(2,794		)	(1,469		)
Effect of federal tax law change	82,767			—			—
Other adjustments - ASU 2016-09 adoption	6,135			—			—
Change in the valuation allowance	(19,198		)	48,096			39,291
Convertible note	47,016			—			—
Permanent items	543			53			26
Other	(312		)	1,371			225
Expiring NOLs and credits - 382 Limitation	—			19,066			—
Income tax expense	$	—		$	—		$	—

Schedule of principal components of the Company's deferred tax assets

The principal components of the Company's deferred tax assets are as follows (in thousands):

	December 31,
	2017			2016
Deferred tax assets:
NOL carryforwards	$	207,620		$	193,436
Capitalized research and development	1,411			1,970
Research and development credits	5,313			4,525
Depreciation	37			—
Accrued expenses	3,846			3,109
Stock-based compensation	15,040			14,903
UNICAP	234			—
Allowance for bad debt	346			—
Other	91			55
Gross non-current deferred tax assets	233,938			217,825
Valuation allowance	(233,938		)	(217,825		)
Net non-current deferred tax assets	$	—		$	—
Deferred tax liabilities:
Depreciation	$	—		$	(173	)
Convertible debt	(35,311		)	—
Gross non-current deferred tax liabilities	(35,311		)	(173		)
Valuation allowance	35,311			173
Net non-current deferred tax liabilities	$	—		$	—

Schedule of unrecognized tax benefits

A reconciliation of the beginning and ending amount of unrecognized tax benefit is as follows (in thousands):

	Uncertain Tax Position
Balance at December 31, 2016	$	(78	)
Decreases related to prior year tax positions	(2,042		)
Increases related to prior year tax positions	2,120
Decreases related to current year tax positions	—
Increases related to current year tax positions	1,263
Ending uncertain tax benefits	$	1,263