Segment Information - Revenue from External Customers by Products and Services (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue from External Customer [Line Items]
Revenues	$ 388,248	$ 304,392	$ 314,438	$ 341,145	$ 375,254	$ 351,014	$ 349,675	$ 326,038	$ 1,348,223	$ 1,401,981	$ 1,358,104
Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									100.00%	100.00%	100.00%
Breathing Apparatus
Revenue from External Customer [Line Items]
Revenues									$ 329,179	$ 317,678	$ 324,672
Breathing Apparatus | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									24.00%	23.00%	24.00%
Fixed Gas and Flame Detection
Revenue from External Customer [Line Items]
Revenues									$ 287,414	$ 292,988	$ 262,432
Fixed Gas and Flame Detection | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									21.00%	21.00%	19.00%
Fire Helmets & Protective Apparel
Revenue from External Customer [Line Items]
Revenues									$ 162,207	$ 178,012	$ 169,679
Fire Helmets & Protective Apparel | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									12.00%	13.00%	13.00%
Portable Gas Detection
Revenue from External Customer [Line Items]
Revenues									$ 142,581	$ 169,479	$ 163,716
Portable Gas Detection | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									11.00%	12.00%	12.00%
Head Protection
Revenue from External Customer [Line Items]
Revenues									$ 125,921	$ 145,403	$ 146,388
Head Protection | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									9.00%	10.00%	11.00%
Fall Protection
Revenue from External Customer [Line Items]
Revenues									$ 103,075	$ 125,869	$ 109,472
Fall Protection | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									8.00%	9.00%	8.00%
Other
Revenue from External Customer [Line Items]
Revenues									$ 197,846	$ 172,552	$ 181,745
Other | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									15.00%	12.00%	13.00%
Americas
Revenue from External Customer [Line Items]
Revenues									$ 874,305	$ 915,118	$ 854,287
Americas | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									100.00%	100.00%	100.00%
Americas | Breathing Apparatus
Revenue from External Customer [Line Items]
Revenues									$ 220,650	$ 212,463	$ 205,100
Americas | Breathing Apparatus | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									25.00%	23.00%	24.00%
Americas | Fixed Gas and Flame Detection
Revenue from External Customer [Line Items]
Revenues									$ 158,924	$ 159,892	$ 135,922
Americas | Fixed Gas and Flame Detection | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									18.00%	17.00%	16.00%
Americas | Fire Helmets & Protective Apparel
Revenue from External Customer [Line Items]
Revenues									$ 133,653	$ 142,043	$ 136,794
Americas | Fire Helmets & Protective Apparel | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									15.00%	16.00%	16.00%
Americas | Portable Gas Detection
Revenue from External Customer [Line Items]
Revenues									$ 90,545	$ 113,914	$ 109,401
Americas | Portable Gas Detection | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									10.00%	12.00%	13.00%
Americas | Head Protection
Revenue from External Customer [Line Items]
Revenues									$ 92,075	$ 112,673	$ 114,465
Americas | Head Protection | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									11.00%	12.00%	13.00%
Americas | Fall Protection
Revenue from External Customer [Line Items]
Revenues									$ 58,060	$ 78,054	$ 61,289
Americas | Fall Protection | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									7.00%	9.00%	7.00%
Americas | Other
Revenue from External Customer [Line Items]
Revenues									$ 120,398	$ 96,079	$ 91,316
Americas | Other | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									14.00%	11.00%	11.00%
International
Revenue from External Customer [Line Items]
Revenues									$ 473,918	$ 486,863	$ 503,817
International | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									100.00%	100.00%	100.00%
International | Breathing Apparatus
Revenue from External Customer [Line Items]
Revenues									$ 108,529	$ 105,215	$ 119,572
International | Breathing Apparatus | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									23.00%	22.00%	24.00%
International | Fixed Gas and Flame Detection
Revenue from External Customer [Line Items]
Revenues									$ 128,490	$ 133,096	$ 126,510
International | Fixed Gas and Flame Detection | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									27.00%	27.00%	25.00%
International | Fire Helmets & Protective Apparel
Revenue from External Customer [Line Items]
Revenues									$ 28,554	$ 35,969	$ 32,885
International | Fire Helmets & Protective Apparel | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									6.00%	7.00%	6.00%
International | Portable Gas Detection
Revenue from External Customer [Line Items]
Revenues									$ 52,036	$ 55,565	$ 54,315
International | Portable Gas Detection | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									11.00%	11.00%	11.00%
International | Head Protection
Revenue from External Customer [Line Items]
Revenues									$ 33,846	$ 32,730	$ 31,923
International | Head Protection | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									7.00%	7.00%	6.00%
International | Fall Protection
Revenue from External Customer [Line Items]
Revenues									$ 45,015	$ 47,815	$ 48,183
International | Fall Protection | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									10.00%	10.00%	10.00%
International | Other
Revenue from External Customer [Line Items]
Revenues									$ 77,448	$ 76,473	$ 90,429
International | Other | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									16.00%	16.00%	18.00%