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Basis of Presentation and Summary of Significant Accounting Policies - Concentration of Risk (Detail)	12 Months Ended
	Dec. 31, 2017 Client Supplier	Dec. 31, 2016 Client Supplier	Dec. 31, 2015 Client
Gross Billings
Concentration Risk [Line Items]
Number of client	3	3	2
Gross Billings | Customer One
Concentration Risk [Line Items]
Concentration risk, percentage	22.00%	15.00%	12.00%
Gross Billings | Customer Two
Concentration Risk [Line Items]
Concentration risk, percentage	11.00%	13.00%	12.00%
Gross Billings | Customer Three
Concentration Risk [Line Items]
Concentration risk, percentage	10.00%	11.00%
Consolidated Accounts Receivable
Concentration Risk [Line Items]
Number of client	3	3
Consolidated Accounts Receivable | Customer One
Concentration Risk [Line Items]
Concentration risk, percentage	33.00%	27.00%
Consolidated Accounts Receivable | Customer Two
Concentration Risk [Line Items]
Concentration risk, percentage	14.00%	13.00%
Consolidated Accounts Receivable | Customer Three
Concentration Risk [Line Items]
Concentration risk, percentage	11.00%	12.00%
Trade Accounts Payables | Supplier Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	12.00%	10.00%
Number of supplier | Supplier	1	1

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Number of client.

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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.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13531-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6404-108592

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13537-108611

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