Acquisitions - Shooter Detection Systems - Consideration Paid and Fair Value of Assets Acquired (Details) - USD ($) $ in Thousands	Dec. 14, 2020	Jun. 30, 2021	Dec. 31, 2020
Tangible and Intangible Net Assets:
Goodwill		$ 112,901	$ 112,838
Shooter Detection Systems
Calculation of Purchase Consideration:
Cash paid, net of working capital adjustment	$ 26,577
Total consideration	26,577
Tangible and Intangible Net Assets:
Cash	311
Accounts receivable	1,179
Inventory	917
Other current assets	240
Property and equipment	77
Operating lease right-of-use assets	384
Other assets	348
Accounts payable	(19)
Accrued expenses	(111)
Operating lease current liabilities	(51)
Operating lease liabilities	(333)
Goodwill	7,239
Total tangible and intangible net assets	26,577
Customer Relationships | Shooter Detection Systems
Tangible and Intangible Net Assets:
Intangible assets acquired	2,362
Developed Technology | Shooter Detection Systems
Tangible and Intangible Net Assets:
Intangible assets acquired	13,522
Trade Name | Shooter Detection Systems
Tangible and Intangible Net Assets:
Intangible assets acquired	$ 512