american tower corporation and subsidiaries notes to consolidated financial statements 2014 ( continued ) basis step-up from corporate restructuring represents the tax effects of increasing the basis for tax purposes of certain of the company 2019s assets in conjunction with its spin-off from american radio systems corporation , its former parent company . at december 31 , 2006 , the company had net federal and state operating loss carryforwards available to reduce future taxable income of approximately $ 2.1 billion and $ 2.5 billion , respectively . if not utilized , the company 2019s net operating loss carryforwards expire as follows ( in thousands ) : .
what portion of state operating loss carryforwards expire between 2017 and 2021?
sfas no . 109 , 201caccounting for income taxes , 201d requires that companies record a valuation allowance when it is 201cmore likely than not that some portion or all of the deferred tax assets will not be realized . 201d at december 31 , 2006 , the company has provided a valuation allowance of approximately $ 308.2 million , including approximately $ 153.6 million attributable to spectrasite , primarily related to net operating loss and capital loss carryforwards assumed as of the acquisition date . the balance of the valuation allowance primarily relates to net state deferred tax assets . the company has not provided a valuation allowance for the remaining deferred tax assets , primarily its federal net operating loss carryforwards , as management believes the company will have sufficient time to realize these federal net operating loss carryforwards during the twenty-year tax carryforward period . valuation allowances may be reversed if related deferred tax assets are deemed realizable based on changes in facts and circumstances relevant to the assets 2019 recoverability . approximately $ 148.3 million of the spectrasite valuation allowances as of december 31 , 2006 will be recorded as a reduction to goodwill if the underlying deferred tax assets are utilized . the company intends to recover a portion of its deferred tax asset through its federal income tax refund claims related to the carry back of certain federal net operating losses . in june 2003 and october 2003 , the company filed federal income tax refund claims with the irs relating to the carry back of $ 380.0 million of net operating losses generated prior to 2003 , of which the company initially anticipated receiving approximately $ 90.0 million . based on preliminary discussions with tax authorities , the company revised its estimate of the net realizable value of the federal income tax refund claims during the year ended december 31 , 2005 , and anticipates receiving a refund of approximately $ 65.0 million , plus interest . the company expects settlement of this matter in the first half of 2007 , however , there can be no assurances with respect to the timing of any refund . because of the uncertainty associated with the claim , the company has not recognized any amounts related to interest . the recoverability of the company 2019s remaining net deferred tax asset has been assessed utilizing stable state ( no growth ) projections based on its current operations . the projections show a significant decrease in depreciation in the later years of the carryforward period as a result of a significant portion of its assets being fully depreciated during the first fifteen years of the carryforward period . accordingly , the recoverability of the net deferred tax asset is not dependent on material improvements to operations , material asset sales or other non-routine transactions . based on its current outlook of future taxable income during the carryforward period , management believes that the net deferred tax asset will be realized . the realization of the company 2019s deferred tax assets as of december 31 , 2006 will be dependent upon its ability to generate approximately $ 1.4 billion in taxable income from january 1 , 2007 to december 31 , 2026 . if the company is unable to generate sufficient taxable income in the future , or carry back losses , as described above , it .