Acquisitions - Business Combination, Pro Forma Information (Details) - OptimalPlus Ltd - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Business Acquisition [Line Items]
Net sales	$ 309,142	$ 348,401	$ 929,381	$ 1,009,102
Net (loss) attributable to NI	$ 4,907	$ 42,522	$ 123,766	$ 65,796