Acquisitions and Dispositions - Fair Value, Valuation Techniques and Related Unobservable Inputs (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Client Relationships
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Value		$ 11.0
Trade Names
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Value		1.4
Non-Compete Agreements
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Value		1.7
Precision Dialogue Holdings, LLC | Client Relationships | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Nonrecurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Value		$ 11.0
Valuation Technique	Excess earnings
Discount rate		16.00%
Precision Dialogue Holdings, LLC | Client Relationships | Fair Value, Inputs, Level 3 | Minimum | Fair Value, Measurements, Nonrecurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Attrition rate		7.00%
Precision Dialogue Holdings, LLC | Client Relationships | Fair Value, Inputs, Level 3 | Maximum | Fair Value, Measurements, Nonrecurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Attrition rate		8.00%
Precision Dialogue Holdings, LLC | Trade Names | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Nonrecurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Value		$ 1.4
Valuation Technique	Relief-from-royalty method
Discount rate		16.00%
Precision Dialogue Holdings, LLC | Trade Names | Fair Value, Inputs, Level 3 | Minimum | Fair Value, Measurements, Nonrecurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Royalty rate (pre-tax)		0.75%
Precision Dialogue Holdings, LLC | Trade Names | Fair Value, Inputs, Level 3 | Maximum | Fair Value, Measurements, Nonrecurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Royalty rate (pre-tax)		1.25%
Precision Dialogue Holdings, LLC | Technology | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Nonrecurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Value		$ 0.6
Valuation Technique	Relief-from-royalty method
Discount rate		16.00%
Royalty rate (pre-tax)		15.00%
Precision Dialogue Holdings, LLC | Technology | Fair Value, Inputs, Level 3 | Minimum | Fair Value, Measurements, Nonrecurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Obsolescence factor		0.00%
Precision Dialogue Holdings, LLC | Technology | Fair Value, Inputs, Level 3 | Maximum | Fair Value, Measurements, Nonrecurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Obsolescence factor		40.00%
Precision Dialogue Holdings, LLC | Non-Compete Agreements | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Nonrecurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Value		$ 1.7
Valuation Technique	With or without method
Discount rate		16.00%