Goodwill and Other Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions			3 Months Ended		6 Months Ended
	May 01, 2017	Mar. 07, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Goodwill And Other Intangible Asset [Line Items]
Amortization expense for finite-lived intangible asset			$ 14.5	$ 16.9	$ 28.7	$ 33.3
Callpointe.com, Inc. [Member]
Goodwill And Other Intangible Asset [Line Items]
Finite-lived intangible assets acquisition date					May 02, 2017
Callpointe.com, Inc. [Member] \| Customer Relationships [Member]
Goodwill And Other Intangible Asset [Line Items]
Finite-lived intangible assets acquired	$ 9.0
Amortization period by major intangible asset class	15 years
Callpointe.com, Inc. [Member] \| Technology [Member]
Goodwill And Other Intangible Asset [Line Items]
Finite-lived intangible assets acquired	$ 2.6
Amortization period by major intangible asset class	3 years
Callpointe.com, Inc. [Member] \| Non-Compete Agreements [Member]
Goodwill And Other Intangible Asset [Line Items]
Finite-lived intangible assets acquired	$ 0.9
Amortization period by major intangible asset class	5 years
Callpointe.com, Inc. [Member] \| Trademarks [Member]
Goodwill And Other Intangible Asset [Line Items]
Finite-lived intangible assets acquired	$ 0.2
Amortization period by major intangible asset class	2 years
Vocus [Member]
Goodwill And Other Intangible Asset [Line Items]
Finite-lived intangible assets acquisition date					Mar. 07, 2017
Vocus [Member] \| Technology [Member]
Goodwill And Other Intangible Asset [Line Items]
Finite-lived intangible assets acquired		$ 0.6
Amortization period by major intangible asset class		4 years
Vocus [Member] \| Non-Compete Agreements [Member]
Goodwill And Other Intangible Asset [Line Items]
Finite-lived intangible assets acquired		$ 0.1
Amortization period by major intangible asset class		3 years

WEST CORP 10-Q