Segment Reporting, Geographic and Customer Information - Additional Information (Detail) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($) Customer	Jun. 30, 2016 USD ($) Customer	Jun. 30, 2017 USD ($) Segment Customer	Jun. 30, 2016 USD ($) Customer
Segment Reporting Information [Line Items]
Number of operating segments			5
Number of reportable segments			4
Gain (loss) on foreign currency exchange rate of west corporation or any of its subsidiaries | $	$ (1.5)	$ 1.1	$ (3.4)	$ (1.0)
Revenues [Member] | Geographic Concentration Risk [Member] | Non-U.S Countries [Member]
Segment Reporting Information [Line Items]
Percentages of consolidated revenue	19.00%	21.00%	19.00%	21.00%
Revenues [Member] | Geographic Concentration Risk [Member] | United Kingdom [Member]
Segment Reporting Information [Line Items]
Percentages of consolidated revenue	11.00%	13.00%	11.00%	13.00%
Revenues [Member] | Geographic Concentration Risk [Member] | United Kingdom [Member] | Minimum [Member]
Segment Reporting Information [Line Items]
Percentages of consolidated revenue			10.00%
Revenues [Member] | Customer Concentration Risk [Member]
Segment Reporting Information [Line Items]
Percentages of consolidated revenue	42.00%	41.00%	43.00%	42.00%
Number of customers | Customer	100	100	100	100
Revenues [Member] | Customer Concentration Risk [Member] | Maximum [Member]
Segment Reporting Information [Line Items]
Percentages of consolidated revenue	6.00%	6.00%	6.00%	6.00%