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Summary of Significant Accounting Policies - Significant Estimates Used by Management in Determining Fair Values of Company's Reporting Units (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Line Items]
Years of cash flows before terminal value	5 years	5 years	5 years
Discounted cash flows	70.00%	70.00%	70.00%
Market multiple	15.00%	15.00%	15.00%
Market capitalization	15.00%	15.00%	15.00%
Minimum
Goodwill [Line Items]
Discount rates	12.00%	12.50%	12.00%
EBITDA multiples	5.5	5.5	5.0
Maximum
Goodwill [Line Items]
Discount rates	14.00%	14.50%	16.00%
EBITDA multiples	7.0	7.0	6.5

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Percentage of the discounted cash flow valuation model used in determining fair value.

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Goodwill Impairment Testing Assumptions [Line Items]

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- Definition

Percentage of the market capitalization valuation model used in determining fair value.

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Percentage of the market multiple valuation model used in determining fair value.

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Years of cash flows before terminal value.

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- Definition

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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Market valuation of entity divided by earnings before interest, taxes, depreciation, and amortization (EBITDA), used as an input to measure fair value.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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