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Summary of Significant Accounting Policies - Additional Information - Concentration of Credit Risk (Detail)	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Services Revenue [Member] | Customer Concentration Risk [Member] | Minimum [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	10.00%		10.00%
Services Revenue [Member] | Customer Concentration Risk [Member] | Medicare [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	42.00%	28.00%
Accounts Receivable [Member] | Credit Concentration Risk [Member] | Minimum [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	10.00%		10.00%
Accounts Receivable [Member] | Credit Concentration Risk [Member] | Medicare [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	19.00%		16.00%

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+ 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
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-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13537-108611

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