Segment Reporting, Geographic and Customer Information - Financial Information of Reportable Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Revenue:
REVENUE	$ 571,407	$ 574,448	$ 1,724,583	$ 1,711,829
Depreciation and Amortization (Included in Operating Income):
Depreciation and amortization	48,335	47,252	145,737	140,915
Operating Income:
OPERATING INCOME	109,499	124,354	341,524	351,480
Cash Capital Expenditures:
Cash Capital Expenditures	25,439	31,319	99,303	96,182
Assets:
Assets	3,477,340		3,477,340		$ 3,555,217
Continuing Operations [Member]
Assets:
Assets	3,477,340		3,477,340		3,537,545
Assets Held For Sale [Member]
Assets:
Assets					17,672
Operating Segments [Member] | Unified Communications Services [Member]
Revenue:
REVENUE	352,377	365,822	1,085,248	1,109,931
Depreciation and Amortization (Included in Operating Income):
Depreciation and amortization	20,726	20,734	62,333	61,844
Operating Income:
OPERATING INCOME	79,406	95,832	257,236	289,668
Cash Capital Expenditures:
Cash Capital Expenditures	7,291	9,333	33,661	41,573
Operating Segments [Member] | Unified Communications Services [Member] | Continuing Operations [Member]
Assets:
Assets	1,484,403		1,484,403		1,525,890
Operating Segments [Member] | Safety Services [Member]
Revenue:
REVENUE	75,061	73,812	220,648	208,528
Depreciation and Amortization (Included in Operating Income):
Depreciation and amortization	10,602	11,918	33,254	36,936
Operating Income:
OPERATING INCOME	17,148	10,248	37,992	16,704
Cash Capital Expenditures:
Cash Capital Expenditures	4,369	6,383	26,851	18,687
Operating Segments [Member] | Safety Services [Member] | Continuing Operations [Member]
Assets:
Assets	767,512		767,512		786,447
Operating Segments [Member] | Interactive Services [Member]
Revenue:
REVENUE	76,439	68,237	221,400	194,332
Depreciation and Amortization (Included in Operating Income):
Depreciation and amortization	9,404	7,670	27,729	22,106
Operating Income:
OPERATING INCOME	9,797	6,220	21,563	18,424
Cash Capital Expenditures:
Cash Capital Expenditures	5,923	5,809	16,072	14,279
Operating Segments [Member] | Interactive Services [Member] | Continuing Operations [Member]
Assets:
Assets	443,819		443,819		430,793
Operating Segments [Member] | Specialized Agent Services [Member]
Revenue:
REVENUE	70,255	68,196	206,128	203,840
Depreciation and Amortization (Included in Operating Income):
Depreciation and amortization	7,603	6,930	22,421	20,029
Operating Income:
OPERATING INCOME	4,372	6,742	11,796	24,269
Cash Capital Expenditures:
Cash Capital Expenditures	2,738	3,632	8,298	9,512
Operating Segments [Member] | Specialized Agent Services [Member] | Continuing Operations [Member]
Assets:
Assets	465,609		465,609		491,449
Eliminations [Member]
Revenue:
REVENUE	(2,725)	(1,619)	(8,841)	(4,802)
Corporate Other-Unallocated [Member]
Operating Income:
OPERATING INCOME	(1,224)	5,312	12,937	2,415
Cash Capital Expenditures:
Cash Capital Expenditures	5,118	$ 6,162	14,421	$ 12,131
Corporate Other-Unallocated [Member] | Continuing Operations [Member]
Assets:
Assets	$ 315,997		$ 315,997		$ 302,966