Goodwill and Other Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
	Mar. 14, 2016	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Goodwill And Other Intangible Asset [Line Items]
Amortization expense for finite-lived intangible asset		$ 16.9	$ 16.4	$ 33.3	$ 33.0
Synrevoice [Member]
Goodwill And Other Intangible Asset [Line Items]
Finite-lived intangible assets acquisition date				Mar. 14, 2016
Synrevoice [Member] | Client Relationships [Member]
Goodwill And Other Intangible Asset [Line Items]
Finite-lived intangible assets acquired	$ 5.3
Amortization period by major intangible asset class	12 years
Synrevoice [Member] | Technology [Member]
Goodwill And Other Intangible Asset [Line Items]
Finite-lived intangible assets acquired	$ 0.9
Amortization period by major intangible asset class	2 years
Synrevoice [Member] | Non-Compete Agreements [Member]
Goodwill And Other Intangible Asset [Line Items]
Finite-lived intangible assets acquired	$ 0.2
Amortization period by major intangible asset class	3 years
Synrevoice [Member] | Trademarks [Member]
Goodwill And Other Intangible Asset [Line Items]
Finite-lived intangible assets acquired	$ 0.1
Amortization period by major intangible asset class	2 years