9. Income Taxes

The following table presents components of loss before income taxes for the periods presented (in thousands):



	Year Ended December 31,
	2016			2015			2014
United States	$	(12,222	)	$	(26,305	)	$	(37,657	)
International	416			528			(44		)
Loss before income taxes	$	(11,806	)	$	(25,777	)	$	(37,701	)

Provision for income taxes for the periods presented consisted of (in thousands):



	Year Ended December 31,
	2016		2015		2014
Current:
U.S. federal	$	—	$	—	$	—
U.S. state	16		21		12
Foreign	38		40		73
Total provision for income taxes	$	54	$	61	$	85

Income tax expense differed from the amounts computed by applying the U.S. federal income tax rate of 34% to pre-tax loss for the periods presented as a result of the following (in thousands):



	Year Ended December 31,
	2016			2015			2014
U.S. federal tax at statutory rate	$	(4,014	)	$	(8,764	)	$	(12,818	)
U.S. state income taxes	490			(756		)	(1,098		)
Non-deductible expenses	931			438			420
Research and development credit	(262		)	(440		)	(455		)
Stock-based compensation	983			737			746
Other	(104		)	481			(72		)
Change in valuation allowance	2,030			8,365			13,362
Total provision for income taxes	$	54		$	61		$	85

The tax effects of temporary differences that give rise to significant portions of the Company’s deferred tax assets and liabilities as of December 31, 2016 and 2015 related to the following (in thousands):



	December 31,
	2016			2015
Deferred tax assets:
Net operating loss and credit carryforwards	$	48,533		$	45,671
Accrued liabilities	3,801			5,488
Allowance for doubtful accounts	429			394
Property and equipment	183			—
Deferred revenue	23			—
Accrued compensation	1,183			817
Intangibles	14			23
Gross deferred tax assets	54,166			52,393
Valuation allowance	(53,598		)	(51,568		)
Net deferred tax assets	568			825
Deferred tax liabilities:
Property and equipment	—			(71		)
Amortized intangibles	(568		)	(754		)
Gross deferred tax liabilities	(568		)	(825		)
Net deferred taxes	$	—		$	—

The Company has not provided for U.S. income taxes on undistributed earnings of its foreign subsidiaries because it intends to permanently re-invest those earnings outside the United States. As of December 31, 2016, undistributed earnings of the Company's foreign subsidiaries was approximately $1.2 million.

A valuation allowance is provided for deferred tax assets where the recoverability of the assets is uncertain. The determination to provide a valuation allowance is dependent upon the assessment of whether it is more likely than not that sufficient future taxable income will be generated to utilize the deferred tax assets. Based on the weight of the available evidence, which includes the Company’s historical operating losses, lack of taxable income, and the accumulated deficit, for the year ended December 31, 2016, the Company has provided a valuation allowance against its U.S. net deferred tax assets. The net change in the valuation allowance for the years ended December 31, 2016 and 2015 was an increase of $2.0 million and $8.4 million, respectively.

As of December 31, 2016, the Company had net operating loss carry-forwards for federal and state income tax purposes of approximately $142.1 million and $79.9 million, respectively, available to reduce future income subject to income taxes. If not utilized, these carryforwards will begin to expire in 2024 for federal purposes and 2017 for state purposes. As of December 31, 2016, the Company also had research credit carryforwards for federal and California state tax purposes of approximately $2.5 million and $2.1 million. If not utilized, the federal research credit carryforwards will begin to expire in 2022. The California state research credits can be carried forward indefinitely. The Internal Revenue Code of 1986, as amended, imposes restrictions on the utilization of net operating losses in the event of an “ownership change” of a corporation. Accordingly, a company’s ability to use net operating losses may be limited as prescribed under the IRC Section 382. Events which may cause limitations in the amount of the net operating losses that the Company may use in any one year include, but are not limited to, a cumulative ownership change of more than 50% over a three-year period. Utilization of the federal and state net operating losses may be subject to substantial annual limitation due to the ownership change limitations provided by the IRC Section 382 and similar state provisions. The Company experienced an ownership change prior to 2014 that did not materially impact the availability of its net operating losses and tax credits and the disclosed amounts of such attributes have been reduced for the effect of the IRC Section 382 limitations. In the event the Company has subsequent changes in ownership in connection with the IPO or other transactions, net operating losses and research and development credit carryforwards, which are fully reserved by the deferred tax asset valuation allowance, could be limited and may expire unutilized.

Unrecognized Tax Benefits

The table below shows the changes in the gross amount of unrecognized tax benefits for the periods presented (in thousands):



	Year Ended December 31,
	2016			2015			2014
Unrecognized benefit — beginning of period	$	2,485		$	1,975		$	1,455
Gross increases — current year tax positions	324			522			532
Gross decreases — prior year tax positions	(4		)	(12		)	(12		)
Unrecognized benefit — end of period	$	2,805		$	2,485		$	1,975

As of December 31, 2016 and 2015, an immaterial amount of the total unrecognized tax benefits, if recognized, would have an impact on the Company’s effective tax rate. The Company recognizes interest and penalties related to uncertain tax positions as income tax expense. The Company does not anticipate that its total unrecognized tax benefits as of December 31, 2016 will significantly change due to settlement of examination or the expiration of statute of limitations during the next 12 months. The Company is currently unaware of any uncertain tax positions that could result in significant additional payments, accruals or other material deviation in this estimate over the next 12 months.

The Company is subject to taxation in the United States, various states and several foreign jurisdictions. Due to the Company’s net carryover of unused operating losses, all years from 2001 forward remain subject to future examination by the U.S. federal and state tax authorities. The Company’s foreign tax returns are open to audit under the statutes of limitations of the respective foreign countries in which the subsidiaries are located. The Company considers all undistributed earnings of its foreign subsidiaries indefinitely reinvested.