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Income Taxes - Summary of Changes in Valuation Allowance for Deferred Tax Assets (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Income Tax Disclosure [Abstract] |  |
Valuation allowance as of beginning of year | $ (17,152) | $ (6,157)
Increases recorded to income tax provision | (7,367) | (10,995)
Valuation allowance as of end of year | $ (24,519) | $ (17,152)

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- Definition Valuation allowance deferred tax asset increase in amount. + References No definition available. + Details
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Namespace Prefix: | spro_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration