Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block]

The domestic and foreign components of income before income taxes were as follows (in thousands):

	Year Ended December 31,
	2019		2018		2017
	(in thousands)
Domestic	$	116,676	$	92,153	$	52,806
Foreign	—		—		—
Income before income taxes	$	116,676	$	92,153	$	52,806

Schedule of Components of Income Tax (Benefit)

The income tax expense (benefit) for the year ended December 31, 2019, 2018 and 2017 consisted of the following:

	Year Ended December 31,
	2019		2018			2017
	(in thousands)
U.S. federal taxes:
Current	$	1,716	$	—		$	—
Deferred	15,944		14,243			(71,839		)
Total U.S. federal taxes	17,660		14,243			(71,839		)
State taxes:
Current	3,900		2,676			388
Deferred	935		(176		)	(4,865		)
Total state taxes	4,835		2,500			(4,477		)
Total	$	22,495	$	16,743		$	(76,316	)

Schedule of Significant Components of Deferred Tax Assets

	Year Ended December 31,
	2019			2018
Deferred tax assets:	(in thousands)
Federal and state net operating losses	$	7,391		$	23,551
Capitalized research and patent costs	7,317			10,260
Research credits	26,164			24,771
Stock-based compensation costs	12,026			9,124
Operating lease liability	857			—
Other	4,186			6,137
Total deferred tax assets	57,941			73,843
Valuation allowance	(11,410		)	(11,184		)
Deferred tax liabilities
Operating lease right-of-use asset	(854		)	—
Total deferred tax liabilities	(854		)	—
Net deferred tax assets	$	45,677		$	62,659

Schedule of Reconciliation of Statutory Federal Income Tax Rate to Effective Rate

The following table presents a reconciliation from the statutory federal income tax rate to the effective rate.

	Year Ended December 31,
	2019			2018			2017
	(in thousands)
U.S. federal taxes at statutory rate	$	24,502		$	19,354		$	17,954
Changes in valuation allowance	—			—			(119,765		)
Federal tax rate change impact to change in valuation allowance	—			—			33,233
R&D and other credits	(4,504		)	(2,178		)	(1,199		)
State income taxes	3,819			1,975			(2,955		)
Non-deductible compensation	657			394			33
Stock-based compensation	(2,107		)	(3,165		)	(3,826		)
Other	128			363			209
Total	$	22,495		$	16,743		$	(76,316	)

Schedule of Changes in Balance of Gross Unrecognized Tax Benefits

The aggregate annual changes in the balance of gross unrecognized tax benefits are as follows (in thousands):

	Year Ended December 31,
	2019		2018			2017
Beginning Balance	$	4,756	$	4,139		$	3,527
Increase in tax positions for prior years	261		—			150
Decrease in tax positions for prior years	—		(135		)	—
Increase in tax positions for current year	1,012		752			462
Decrease in tax positions for current year	—		—			—
Ending Balance	$	6,029	$	4,756		$	4,139