Segment Reporting, Geographic and Customer Information - Financial Information of Reportable Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Revenue:
REVENUE	$ 574,393	$ 582,397	$ 1,146,935	$ 1,153,176
Depreciation and Amortization (Included in Operating Income):
Depreciation and amortization	46,383	48,907	92,816	97,402
Operating Income:
OPERATING INCOME	102,602	123,101	210,825	232,025
Cash Capital Expenditures:
Cash Capital Expenditures	26,576	37,507	53,248	73,864
Assets:
Assets	3,480,945		3,480,945		$ 3,440,838
Operating Segments [Member] | Unified Communications Services [Member]
Revenue:
REVENUE	348,546	370,158	699,621	732,871
Depreciation and Amortization (Included in Operating Income):
Depreciation and amortization	18,515	20,671	37,132	41,607
Operating Income:
OPERATING INCOME	72,020	88,762	153,410	177,830
Cash Capital Expenditures:
Cash Capital Expenditures	11,618	13,337	24,267	26,370
Operating Segments [Member] | Unified Communications Services [Member] | Continuing Operations [Member]
Assets:
Assets	1,441,976		1,441,976		1,459,919
Operating Segments [Member] | Safety Services [Member]
Revenue:
REVENUE	80,419	74,423	156,674	145,587
Depreciation and Amortization (Included in Operating Income):
Depreciation and amortization	10,413	11,446	20,749	22,652
Operating Income:
OPERATING INCOME	20,897	11,871	40,183	20,844
Cash Capital Expenditures:
Cash Capital Expenditures	2,153	11,764	5,939	22,482
Operating Segments [Member] | Safety Services [Member] | Continuing Operations [Member]
Assets:
Assets	764,855		764,855		772,308
Operating Segments [Member] | Interactive Services [Member]
Revenue:
REVENUE	79,179	73,232	156,672	144,961
Depreciation and Amortization (Included in Operating Income):
Depreciation and amortization	9,745	9,350	19,491	18,325
Operating Income:
OPERATING INCOME	7,828	5,958	16,183	11,766
Cash Capital Expenditures:
Cash Capital Expenditures	5,126	6,350	9,753	10,149
Operating Segments [Member] | Interactive Services [Member] | Continuing Operations [Member]
Assets:
Assets	468,241		468,241		430,722
Operating Segments [Member] | Specialized Agent Services [Member]
Revenue:
REVENUE	69,354	67,495	141,102	135,873
Depreciation and Amortization (Included in Operating Income):
Depreciation and amortization	7,710	7,440	15,444	14,818
Operating Income:
OPERATING INCOME	4,531	2,906	8,089	7,424
Cash Capital Expenditures:
Cash Capital Expenditures	1,991	2,603	3,842	5,560
Operating Segments [Member] | Specialized Agent Services [Member] | Continuing Operations [Member]
Assets:
Assets	458,170		458,170		468,384
Eliminations [Member]
Revenue:
REVENUE	(3,105)	(2,911)	(7,134)	(6,116)
Corporate Other-Unallocated [Member]
Operating Income:
OPERATING INCOME	(2,674)	13,604	(7,040)	14,161
Cash Capital Expenditures:
Cash Capital Expenditures	5,688	$ 3,453	9,447	$ 9,303
Corporate Other-Unallocated [Member] | Continuing Operations [Member]
Assets:
Assets	$ 347,703		$ 347,703		$ 309,505