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Debt - Summary of Amendment to Senior Secured Revolving Credit Facility (Descriptors) (Details)	12 Months Ended
	Dec. 31, 2018 USD ($)
Senior Secured Notes [Line Items]
Amounts which can be increased to the credit facility, subject to lender approval (up to)	$ 150,000,000
Minimum | LIBOR
Senior Secured Notes [Line Items]
Line of credit, interest spread basis points (in percentage)	1.55%
Maximum | LIBOR
Senior Secured Notes [Line Items]
Line of credit, interest spread basis points (in percentage)	2.30%

X

- Definition

Amounts which can be increased to the credit facility, subject to lender approval.

+ References

No definition available.

+ Details

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Balance Type:	credit
Period Type:	duration

X

- Definition

Line Of Credit Facility Basis Spread On Variable Rate

+ References

No definition available.

+ Details

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Namespace Prefix:	wfx_
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Balance Type:	na
Period Type:	duration

X

- Definition

Senior Secured Notes [Line Items]

+ References

No definition available.

+ Details

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Namespace Prefix:	wfx_
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Balance Type:	na
Period Type:	duration

X

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

X

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
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Balance Type:
Period Type:

X

- Details

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Namespace Prefix:
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