Acquisitions - Schedule of Recognized Identified Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Apr. 15, 2019	Dec. 31, 2018
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets [Abstract]
Goodwill	$ 1,251,938	$ 1,243,669		$ 1,206,877
Opterna International Corp.
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets [Abstract]
Receivables	$ 5,300		$ 5,308
Inventory			7,359
Prepaid and other current assets			566
Property, plant, and equipment			1,328
Intangible assets			28,000
Goodwill			35,057
Deferred income taxes			80
Operating lease right-of-use assets			2,204
Other long-lived assets			2,070
Total assets acquired			81,972
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities [Abstract]
Accounts payable			4,847
Accrued liabilities			4,301
Long-term deferred tax liability			6,813
Long-term operating lease liability			1,923
Other long-term liabilities			7,152
Total liabilities assumed			25,036
Net assets			56,936
Noncontrolling interest			5,195
Net assets attributable to Belden			$ 51,741