Acquisitions - Schedule of Pro Forma Information (Details) - Opterna International Corp. - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Revenues	$ 2,139,894	$ 2,213,781
Net income (loss) attributable to Belden common stockholders	$ (389,957)	$ 123,546
Diluted income (loss) per share attributable to Belden common stockholders (in dollars per share)	$ (9.24)	$ 3.02