Segment Reporting, Geographic and Customer Information - Financial Information of Reportable Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Revenue:
REVENUE	$ 582,397	$ 571,891	$ 1,153,176	$ 1,137,381
Depreciation and Amortization (Included in Operating Income):
Depreciation and amortization	48,907	46,742	97,402	93,662
Operating Income:
OPERATING INCOME	123,101	116,433	232,025	227,126
Cash Capital Expenditures:
Cash Capital Expenditures	37,507	28,557	73,864	64,864
Assets:
Assets	3,546,601		3,546,601		$ 3,555,217
Continuing Operations [Member]
Assets:
Assets	3,546,601		3,546,601		3,537,545
Assets Held For Sale [Member]
Assets:
Assets					17,672
Operating Segments [Member] | Unified Communications Services [Member]
Revenue:
REVENUE	370,158	374,651	732,871	744,109
Depreciation and Amortization (Included in Operating Income):
Depreciation and amortization	20,671	20,625	41,607	41,108
Operating Income:
OPERATING INCOME	88,762	98,958	177,830	193,836
Cash Capital Expenditures:
Cash Capital Expenditures	13,337	12,341	26,370	32,240
Operating Segments [Member] | Unified Communications Services [Member] | Continuing Operations [Member]
Assets:
Assets	1,492,257		1,492,257		1,525,890
Operating Segments [Member] | Safety Services [Member]
Revenue:
REVENUE	74,423	66,138	145,587	134,716
Depreciation and Amortization (Included in Operating Income):
Depreciation and amortization	11,446	12,210	22,652	25,019
Operating Income:
OPERATING INCOME	11,871	3,254	20,844	6,456
Cash Capital Expenditures:
Cash Capital Expenditures	11,764	6,387	22,482	12,304
Operating Segments [Member] | Safety Services [Member] | Continuing Operations [Member]
Assets:
Assets	771,599		771,599		786,447
Operating Segments [Member] | Interactive Services [Member]
Revenue:
REVENUE	73,232	63,628	144,961	126,095
Depreciation and Amortization (Included in Operating Income):
Depreciation and amortization	9,350	7,282	18,325	14,436
Operating Income:
OPERATING INCOME	5,958	6,630	11,766	12,204
Cash Capital Expenditures:
Cash Capital Expenditures	6,350	4,478	10,149	8,470
Operating Segments [Member] | Interactive Services [Member] | Continuing Operations [Member]
Assets:
Assets	449,626		449,626		430,793
Operating Segments [Member] | Specialized Agent Services [Member]
Revenue:
REVENUE	67,495	68,566	135,873	135,644
Depreciation and Amortization (Included in Operating Income):
Depreciation and amortization	7,440	6,625	14,818	13,099
Operating Income:
OPERATING INCOME	2,906	8,992	7,424	17,527
Cash Capital Expenditures:
Cash Capital Expenditures	2,603	3,104	5,560	5,880
Operating Segments [Member] | Specialized Agent Services [Member] | Continuing Operations [Member]
Assets:
Assets	474,077		474,077		491,449
Eliminations [Member]
Revenue:
REVENUE	(2,911)	(1,092)	(6,116)	(3,183)
Corporate Other-Unallocated [Member]
Operating Income:
OPERATING INCOME	13,604	(1,401)	14,161	(2,897)
Cash Capital Expenditures:
Cash Capital Expenditures	3,453	$ 2,247	9,303	$ 5,970
Corporate Other-Unallocated [Member] | Continuing Operations [Member]
Assets:
Assets	$ 359,042		$ 359,042		$ 302,966