Segment Information - Percentage of Total Sales by Product Group (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenue from External Customer [Line Items]
Revenues	$ 341,145	$ 326,038
Breathing Apparatus
Revenue from External Customer [Line Items]
Revenues	75,844	75,446
Fixed Gas & Flame Detection
Revenue from External Customer [Line Items]
Revenues	69,911	60,398
Firefighter Helmets & Protective Apparel
Revenue from External Customer [Line Items]
Revenues	42,547	43,577
Portable Gas Detection
Revenue from External Customer [Line Items]
Revenues	41,052	40,726
Industrial Head Protection
Revenue from External Customer [Line Items]
Revenues	35,332	35,744
Fall Protection
Revenue from External Customer [Line Items]
Revenues	27,428	30,128
Other
Revenue from External Customer [Line Items]
Revenues	$ 49,031	$ 40,019
Sales
Revenue from External Customer [Line Items]
Concentration risk percentage	100.00%	100.00%
Sales | Breathing Apparatus
Revenue from External Customer [Line Items]
Concentration risk percentage	22.00%	23.00%
Sales | Fixed Gas & Flame Detection
Revenue from External Customer [Line Items]
Concentration risk percentage	21.00%	19.00%
Sales | Firefighter Helmets & Protective Apparel
Revenue from External Customer [Line Items]
Concentration risk percentage	12.00%	13.00%
Sales | Portable Gas Detection
Revenue from External Customer [Line Items]
Concentration risk percentage	12.00%	13.00%
Sales | Industrial Head Protection
Revenue from External Customer [Line Items]
Concentration risk percentage	10.00%	11.00%
Sales | Fall Protection
Revenue from External Customer [Line Items]
Concentration risk percentage	8.00%	9.00%
Sales | Other
Revenue from External Customer [Line Items]
Concentration risk percentage	15.00%	12.00%
Americas
Revenue from External Customer [Line Items]
Revenues	$ 231,253	$ 213,687
Americas | Breathing Apparatus
Revenue from External Customer [Line Items]
Revenues	52,693	50,904
Americas | Fixed Gas & Flame Detection
Revenue from External Customer [Line Items]
Revenues	41,247	32,930
Americas | Firefighter Helmets & Protective Apparel
Revenue from External Customer [Line Items]
Revenues	35,113	35,064
Americas | Portable Gas Detection
Revenue from External Customer [Line Items]
Revenues	27,648	26,991
Americas | Industrial Head Protection
Revenue from External Customer [Line Items]
Revenues	27,555	27,836
Americas | Fall Protection
Revenue from External Customer [Line Items]
Revenues	17,697	17,961
Americas | Other
Revenue from External Customer [Line Items]
Revenues	$ 29,300	$ 22,001
Americas | Sales
Revenue from External Customer [Line Items]
Concentration risk percentage	100.00%	100.00%
Americas | Sales | Breathing Apparatus
Revenue from External Customer [Line Items]
Concentration risk percentage	23.00%	24.00%
Americas | Sales | Fixed Gas & Flame Detection
Revenue from External Customer [Line Items]
Concentration risk percentage	18.00%	15.00%
Americas | Sales | Firefighter Helmets & Protective Apparel
Revenue from External Customer [Line Items]
Concentration risk percentage	15.00%	16.00%
Americas | Sales | Portable Gas Detection
Revenue from External Customer [Line Items]
Concentration risk percentage	12.00%	13.00%
Americas | Sales | Industrial Head Protection
Revenue from External Customer [Line Items]
Concentration risk percentage	12.00%	13.00%
Americas | Sales | Fall Protection
Revenue from External Customer [Line Items]
Concentration risk percentage	8.00%	8.00%
Americas | Sales | Other
Revenue from External Customer [Line Items]
Concentration risk percentage	12.00%	11.00%
International
Revenue from External Customer [Line Items]
Revenues	$ 109,892	$ 112,351
International | Breathing Apparatus
Revenue from External Customer [Line Items]
Revenues	23,151	24,542
International | Fixed Gas & Flame Detection
Revenue from External Customer [Line Items]
Revenues	28,664	27,468
International | Firefighter Helmets & Protective Apparel
Revenue from External Customer [Line Items]
Revenues	7,434	8,513
International | Portable Gas Detection
Revenue from External Customer [Line Items]
Revenues	13,404	13,735
International | Industrial Head Protection
Revenue from External Customer [Line Items]
Revenues	7,777	7,908
International | Fall Protection
Revenue from External Customer [Line Items]
Revenues	9,731	12,167
International | Other
Revenue from External Customer [Line Items]
Revenues	$ 19,731	$ 18,018
International | Sales
Revenue from External Customer [Line Items]
Concentration risk percentage	100.00%	100.00%
International | Sales | Breathing Apparatus
Revenue from External Customer [Line Items]
Concentration risk percentage	21.00%	22.00%
International | Sales | Fixed Gas & Flame Detection
Revenue from External Customer [Line Items]
Concentration risk percentage	26.00%	24.00%
International | Sales | Firefighter Helmets & Protective Apparel
Revenue from External Customer [Line Items]
Concentration risk percentage	7.00%	8.00%
International | Sales | Portable Gas Detection
Revenue from External Customer [Line Items]
Concentration risk percentage	12.00%	12.00%
International | Sales | Industrial Head Protection
Revenue from External Customer [Line Items]
Concentration risk percentage	7.00%	7.00%
International | Sales | Fall Protection
Revenue from External Customer [Line Items]
Concentration risk percentage	9.00%	11.00%
International | Sales | Other
Revenue from External Customer [Line Items]
Concentration risk percentage	18.00%	16.00%