Segment Reporting, Geographic and Customer Information - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) Segment	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Foreign Currency Translation [Line Items]
Number of operating segments	5
Number of reportable segments	4
Percentages of revenue	44.00%	47.00%	47.00%
Foreign currency exchange rate of west corporation or any of its subsidiaries | $	$ (2.5)	$ 2.0	$ (4.9)
Customer Concentration Risk [Member] | Sales Revenue, Net [Member] | Maximum [Member]
Foreign Currency Translation [Line Items]
Concentration risk, percentage	10.00%	10.00%	10.00%
United Kingdom [Member]
Foreign Currency Translation [Line Items]
Percentages of consolidated revenue	13.00%	13.00%	12.00%
Aggregate revenue as a percentage of total revenue from largest one client	10.00%	10.00%	10.00%