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Income Taxes - Periods Open to Tax Examination (Details)	12 Months Ended
	Dec. 31, 2018
Minimum
Income Tax Contingency [Line Items]
Number of tax years open for state tax audit (in years)	3 years
Maximum
Income Tax Contingency [Line Items]
Number of tax years open for state tax audit (in years)	5 years

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

X

- Definition

Number of taxable years open for state tax audit

+ References

No definition available.

+ Details

Name:	wfx_NumberOfTaxableYearsOpenForTaxAudit
Namespace Prefix:	wfx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: