Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Income Tax Provision

The income tax provision consists of the following (in thousands):

	Year Ended December 31,
	2019		2018
Current:
Federal	$	—	$	—
State	—		—
Foreign	—		—
	—		—
Deferred:
Federal	$	—	$	—
State	—		—
Foreign	—		—
	—		—
Total provision for income taxes	$	—	$	—

Reconciliation of Effective Tax Rate for the Provision for Income Taxes

The effective tax rate of our provision for income taxes differs from the federal statutory rate as follows:

	Year Ended December 31,
	2019		2018		2017
Federal statutory income tax rate	21.0	%	21.0	%	34.0	%
Federal and state credits	3.2	%	7.4	%	8.9	%
Excess tax benefit	0.3	%	0.4	%	8.6	%
Stock based compensation	(2.5	)%	(0.8	)%	0.1	%
U.S. tax on foreign earnings	(0.2	)%	—	%	—	%
Other	(0.5	)%	(0.6	)%	(0.1	)%
Tax impact due to tax rate reduction	—	%	—	%	(47.7	)%
Change in valuation allowance	(19.8	)%	(24.1	)%	2.6	%
Foreign rate differential	(1.5	)%	(3.3	)%	(6.4	)%
Total tax provision	0.0	%	0.0	%	0.0	%

Components of U.S. Deferred Tax Assets and (Liabilities)

The components of U.S. deferred tax assets and (liabilities) are as follows (in thousands):

	December 31,
	2019			2018
Deferred tax assets:
Federal and state net operating loss carryforwards	$	285,685		$	241,881
Federal and state research tax credit carryforwards	24,782			23,917
Federal Orphan Drug Credit	112,802			120,273
Deferred revenue	44,588			29,530
Stock options	20,893			19,992
Inventories	10,617			4,350
Operating lease liabilities	3,146			—
Other	7,861			5,098
Total deferred tax assets	510,374			445,041
Deferred tax liabilities:
Operating lease right-of-use assets	(2,793		)	—
Total deferred tax liabilities	(2,793		)	—
Net deferred tax assets before valuation allowance	507,581			445,041
Valuation allowance	(507,581		)	(445,041		)
Net deferred tax assets	$	—		$	—

Reconciliation of the Beginning and Ending Amount of Unrecognized Tax Benefits

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

	Year Ended December 31,
	2019			2018			2017
Unrecognized tax benefits, beginning of period	$	25,421		$	20,730		$	13,865
Increases due to current period positions	1,875			4,879			7,046
Increase due to prior period positions	22			26			—
Decreases due to prior period positions	(3,017		)	(214		)	(181		)
Unrecognized tax benefits, end of period	$	24,301		$	25,421		$	20,730