Segment Information - Revenue from External Customers by Products and Services (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue from External Customer [Line Items]
Revenues	$ 375,254	$ 351,014	$ 349,675	$ 326,038	$ 361,783	$ 331,096	$ 339,331	$ 325,894	$ 1,401,981	$ 1,358,104	$ 1,196,809
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									$ 317,678	$ 324,672	$ 292,448
Breathing Apparatus | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									23.00%	24.00%	24.00%
Fixed Gas and Flame Detection
Revenue from External Customer [Line Items]
Revenues									$ 292,988	$ 262,432	$ 248,047
Fixed Gas and Flame Detection | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									21.00%	19.00%	21.00%
Fire Helmets & Protective Apparel
Revenue from External Customer [Line Items]
Revenues									$ 178,012	$ 169,679	$ 103,441
Fire Helmets & Protective Apparel | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									13.00%	13.00%	9.00%
Portable Gas Detection
Revenue from External Customer [Line Items]
Revenues									$ 169,479	$ 163,716	$ 149,063
Portable Gas Detection | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									12.00%	12.00%	12.00%
Head Protection
Revenue from External Customer [Line Items]
Revenues									$ 145,403	$ 146,388	$ 133,180
Head Protection | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									10.00%	11.00%	11.00%
Fall Protection
Revenue from External Customer [Line Items]
Revenues									$ 125,869	$ 109,472	$ 98,929
Fall Protection | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									9.00%	8.00%	8.00%
Other
Revenue from External Customer [Line Items]
Revenues									$ 172,552	$ 181,745	$ 171,701
Other | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									12.00%	13.00%	15.00%
Americas
Revenue from External Customer [Line Items]
Revenues									$ 915,118	$ 854,287	$ 736,847
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									$ 212,463	$ 205,100	$ 191,457
Americas | Breathing Apparatus | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									23.00%	24.00%	26.00%
Americas | Fixed Gas and Flame Detection
Revenue from External Customer [Line Items]
Revenues									$ 159,892	$ 135,922	$ 123,414
Americas | Fixed Gas and Flame Detection | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									17.00%	16.00%	17.00%
Americas | Fire Helmets & Protective Apparel
Revenue from External Customer [Line Items]
Revenues									$ 142,043	$ 136,794	$ 69,767
Americas | Fire Helmets & Protective Apparel | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									16.00%	16.00%	9.00%
Americas | Portable Gas Detection
Revenue from External Customer [Line Items]
Revenues									$ 113,914	$ 109,401	$ 98,580
Americas | Portable Gas Detection | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									12.00%	13.00%	13.00%
Americas | Head Protection
Revenue from External Customer [Line Items]
Revenues									$ 112,673	$ 114,465	$ 105,514
Americas | Head Protection | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									12.00%	13.00%	14.00%
Americas | Fall Protection
Revenue from External Customer [Line Items]
Revenues									$ 78,054	$ 61,289	$ 54,468
Americas | Fall Protection | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									9.00%	7.00%	7.00%
Americas | Other
Revenue from External Customer [Line Items]
Revenues									$ 96,079	$ 91,316	$ 93,647
Americas | Other | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									11.00%	11.00%	14.00%
International
Revenue from External Customer [Line Items]
Revenues									$ 486,863	$ 503,817	$ 459,962
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									$ 105,215	$ 119,572	$ 100,991
International | Breathing Apparatus | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									22.00%	24.00%	22.00%
International | Fixed Gas and Flame Detection
Revenue from External Customer [Line Items]
Revenues									$ 133,096	$ 126,510	$ 124,633
International | Fixed Gas and Flame Detection | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									27.00%	25.00%	27.00%
International | Fire Helmets & Protective Apparel
Revenue from External Customer [Line Items]
Revenues									$ 35,969	$ 32,885	$ 33,674
International | Fire Helmets & Protective Apparel | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									7.00%	6.00%	7.00%
International | Portable Gas Detection
Revenue from External Customer [Line Items]
Revenues									$ 55,565	$ 54,315	$ 50,483
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									$ 32,730	$ 31,923	$ 27,666
International | Head Protection | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									7.00%	6.00%	6.00%
International | Fall Protection
Revenue from External Customer [Line Items]
Revenues									$ 47,815	$ 48,183	$ 44,461
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									$ 76,473	$ 90,429	$ 78,054
International | Other | Sales
Revenue from External Customer [Line Items]
Concentration risk (percentage)									16.00%	18.00%	17.00%