Operating Segments and Related Information (Details 4) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Segment Reporting, Asset Reconciling Item [Line Items]
BU assets (accounts receivable, inventory and demo assets, Net)	$ 704,239		$ 756,425
BU assets (accounts receivable, inventory, demo assets and goodwill, Net)	1,615,499
Cash, cash equivalents and restricted cash	593,335		519,090	$ 436,961	$ 361,349
Assets held for sale, net	0		67,344
Prepaid expenses and other current assets	57,157		44,360
Property and equipment, net	250,050		263,996
Deferred Income Tax Assets, Net	94,440	$ 95,368	21,001
Goodwill	911,260	909,811	909,811
Intangible assets, net	151,778		168,130
Other assets	94,626	58,864	59,869
Assets	2,856,885		2,810,026
Government and Defense
Segment Reporting, Asset Reconciling Item [Line Items]
BU assets (accounts receivable, inventory and demo assets, Net)	297,590		332,044
Goodwill	291,478	291,229
Industrial
Segment Reporting, Asset Reconciling Item [Line Items]
BU assets (accounts receivable, inventory and demo assets, Net)	270,299		287,439
Goodwill	392,472	389,575
Commercial
Segment Reporting, Asset Reconciling Item [Line Items]
BU assets (accounts receivable, inventory and demo assets, Net)	136,350		$ 136,942
Goodwill	$ 227,310	$ 229,007