Segment, Customer Concentration and Geographical Information - Additional Information (Detail)	12 Months Ended
Dec. 31, 2017 Business_Unit Location	Dec. 31, 2016 Location	Dec. 31, 2015 Location
Revenue, Major Customer [Line Items]
Number of primary business units \| Business_Unit	2
Number of geographic locations \| Location	3	3	3
Customer Concentration Risk [Member] \| Accounts Receivable [Member]
Revenue, Major Customer [Line Items]
Concentration percentage	72.00%	80.00%	83.00%
Customer Concentration Risk [Member] \| Accounts Receivable [Member] \| Sprint and Fast Spring [Member]
Revenue, Major Customer [Line Items]
Concentration percentage	72.00%	80.00%	83.00%

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.

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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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration