Fair Value Measurements - Summary of Changes in Fair Value of Company's Level 3 Assets and Liabilities (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Equities [Member]
Fair Value of Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Net unrealized losses	$ 1	$ 0
Contingent Consideration Liability [Member]
Fair Value of Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Net unrealized losses	$ 33	$ 2,745

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.

No definition available.

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- Definition

Amount of unrealized (holding) gain (loss) which is included in the statement of income (or changes in net assets) related to those assets still held at the reporting date for which fair value is measured on a recurring basis using significant unobservable inputs (Level 3).

+ 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 (d)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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- Definition

Amount of unrealized (holding) gain (loss) which is included in the statement of income (or changes in net assets) related to those liabilities still held at the reporting date for which fair value is measured on a recurring basis using significant unobservable inputs (Level 3).

+ References

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