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Long-term Supply Contract (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Jul. 30, 2014
Commitments and Contingencies Disclosure [Abstract]
Supply agreement liability	$ 22,250	$ 23,888	$ 27,300

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- Definition

Long-term Supply Commitment, Amount

+ References

No definition available.

+ Details

Name:	pqg_LongtermSupplyCommitmentAmount
Namespace Prefix:	pqg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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- References

No definition available.

+ Details

Name:	us-gaap_CommitmentsAndContingenciesDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration