Segment Information - Percentage of Total Sales by Product Group (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue from External Customer [Line Items]
Revenues	$ 304,392	$ 351,014	$ 959,975	$ 1,026,726
Breathing Apparatus
Revenue from External Customer [Line Items]
Revenues	62,454	71,312	214,162	221,666
Fixed Gas & Flame Detection
Revenue from External Customer [Line Items]
Revenues	70,038	75,855	205,334	206,564
Firefighter Helmets & Protective Apparel
Revenue from External Customer [Line Items]
Revenues	38,785	42,804	121,669	135,181
Portable Gas Detection
Revenue from External Customer [Line Items]
Revenues	32,701	44,240	102,138	127,309
Industrial Head Protection
Revenue from External Customer [Line Items]
Revenues	29,328	37,730	95,260	112,395
Fall Protection
Revenue from External Customer [Line Items]
Revenues	24,620	34,639	73,707	96,396
Other
Revenue from External Customer [Line Items]
Revenues	$ 46,466	$ 44,434	$ 147,705	$ 127,215
Sales
Revenue from External Customer [Line Items]
Concentration risk percentage	100.00%	100.00%	100.00%	100.00%
Sales | Breathing Apparatus
Revenue from External Customer [Line Items]
Concentration risk percentage	20.00%	20.00%	22.00%	22.00%
Sales | Fixed Gas & Flame Detection
Revenue from External Customer [Line Items]
Concentration risk percentage	23.00%	22.00%	21.00%	20.00%
Sales | Firefighter Helmets & Protective Apparel
Revenue from External Customer [Line Items]
Concentration risk percentage	13.00%	12.00%	13.00%	13.00%
Sales | Portable Gas Detection
Revenue from External Customer [Line Items]
Concentration risk percentage	11.00%	13.00%	11.00%	12.00%
Sales | Industrial Head Protection
Revenue from External Customer [Line Items]
Concentration risk percentage	10.00%	11.00%	10.00%	11.00%
Sales | Fall Protection
Revenue from External Customer [Line Items]
Concentration risk percentage	8.00%	10.00%	8.00%	9.00%
Sales | Other
Revenue from External Customer [Line Items]
Concentration risk percentage	15.00%	12.00%	15.00%	13.00%
Americas
Revenue from External Customer [Line Items]
Revenues	$ 194,303	$ 234,624	$ 629,787	$ 679,699
Americas | Breathing Apparatus
Revenue from External Customer [Line Items]
Revenues	38,889	46,287	141,850	147,776
Americas | Fixed Gas & Flame Detection
Revenue from External Customer [Line Items]
Revenues	39,411	42,953	117,399	115,001
Americas | Firefighter Helmets & Protective Apparel
Revenue from External Customer [Line Items]
Revenues	33,000	35,017	101,857	109,173
Americas | Portable Gas Detection
Revenue from External Customer [Line Items]
Revenues	20,972	30,305	65,822	85,763
Americas | Industrial Head Protection
Revenue from External Customer [Line Items]
Revenues	21,489	29,217	69,549	87,475
Americas | Fall Protection
Revenue from External Customer [Line Items]
Revenues	13,109	22,972	42,185	59,653
Americas | Other
Revenue from External Customer [Line Items]
Revenues	$ 27,433	$ 27,873	$ 91,125	$ 74,858
Americas | Sales
Revenue from External Customer [Line Items]
Concentration risk percentage	100.00%	100.00%	100.00%	100.00%
Americas | Sales | Breathing Apparatus
Revenue from External Customer [Line Items]
Concentration risk percentage	20.00%	20.00%	23.00%	22.00%
Americas | Sales | Fixed Gas & Flame Detection
Revenue from External Customer [Line Items]
Concentration risk percentage	20.00%	18.00%	19.00%	17.00%
Americas | Sales | Firefighter Helmets & Protective Apparel
Revenue from External Customer [Line Items]
Concentration risk percentage	17.00%	15.00%	16.00%	16.00%
Americas | Sales | Portable Gas Detection
Revenue from External Customer [Line Items]
Concentration risk percentage	11.00%	13.00%	10.00%	13.00%
Americas | Sales | Industrial Head Protection
Revenue from External Customer [Line Items]
Concentration risk percentage	11.00%	12.00%	11.00%	13.00%
Americas | Sales | Fall Protection
Revenue from External Customer [Line Items]
Concentration risk percentage	7.00%	10.00%	7.00%	9.00%
Americas | Sales | Other
Revenue from External Customer [Line Items]
Concentration risk percentage	14.00%	12.00%	14.00%	10.00%
International
Revenue from External Customer [Line Items]
Revenues	$ 110,089	$ 116,390	$ 330,188	$ 347,027
International | Breathing Apparatus
Revenue from External Customer [Line Items]
Revenues	23,565	25,025	72,312	73,890
International | Fixed Gas & Flame Detection
Revenue from External Customer [Line Items]
Revenues	30,627	32,902	87,935	91,563
International | Firefighter Helmets & Protective Apparel
Revenue from External Customer [Line Items]
Revenues	5,785	7,787	19,812	26,008
International | Portable Gas Detection
Revenue from External Customer [Line Items]
Revenues	11,729	13,935	36,316	41,546
International | Industrial Head Protection
Revenue from External Customer [Line Items]
Revenues	7,839	8,513	25,711	24,920
International | Fall Protection
Revenue from External Customer [Line Items]
Revenues	11,511	11,667	31,522	36,743
International | Other
Revenue from External Customer [Line Items]
Revenues	$ 19,033	$ 16,561	$ 56,580	$ 52,357
International | Sales
Revenue from External Customer [Line Items]
Concentration risk percentage	100.00%	100.00%	100.00%	100.00%
International | Sales | Breathing Apparatus
Revenue from External Customer [Line Items]
Concentration risk percentage	21.00%	22.00%	22.00%	21.00%
International | Sales | Fixed Gas & Flame Detection
Revenue from External Customer [Line Items]
Concentration risk percentage	28.00%	28.00%	27.00%	26.00%
International | Sales | Firefighter Helmets & Protective Apparel
Revenue from External Customer [Line Items]
Concentration risk percentage	5.00%	7.00%	6.00%	7.00%
International | Sales | Portable Gas Detection
Revenue from External Customer [Line Items]
Concentration risk percentage	11.00%	12.00%	11.00%	12.00%
International | Sales | Industrial Head Protection
Revenue from External Customer [Line Items]
Concentration risk percentage	7.00%	7.00%	8.00%	7.00%
International | Sales | Fall Protection
Revenue from External Customer [Line Items]
Concentration risk percentage	11.00%	10.00%	9.00%	11.00%
International | Sales | Other
Revenue from External Customer [Line Items]
Concentration risk percentage	17.00%	14.00%	17.00%	16.00%