Business Acquisition (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Feb. 11, 2019	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Business Acquisition [Line Items]
Payments to acquire businesses, gross	$ 365,000
Cash	119
Other current assets	9,315
Current assets	9,434
Property, plant & equipment	4,036
Deferred income taxes	80
Goodwill		$ 616,427		$ 616,427		$ 400,440
Other non-current assets	166
Total assets acquired	369,509
Current liabilities assumed	4,462
Total liabilities assumed	4,462
Net assets acquired	365,047
Goodwill, expected tax deductible amount	215,800
Net sales		238,263	$ 222,407	461,660	$ 433,680
Net income (loss)		8,625	1,890	17,370	(1,319)
Net sales		238,263	212,820	456,641	414,884
Cost of Sales
Business Acquisition [Line Items]
Business acquisition costs		503	0	1,163	0
Selling and Administrative Expenses
Business Acquisition [Line Items]
Business acquisition costs		2,461	0	9,706	0
Buffalo Filter LLC
Business Acquisition [Line Items]
Goodwill	$ 215,793
Weighted average amortization period (in years)	16 years
Net sales		$ 13,500		$ 19,500
Customer relationships
Business Acquisition [Line Items]
Intangible assets	$ 124,000
Customer relationships | Buffalo Filter LLC
Business Acquisition [Line Items]
Weighted average amortization period (in years)	16 years
Developed technology
Business Acquisition [Line Items]
Intangible assets	$ 9,000
Developed technology | Buffalo Filter LLC
Business Acquisition [Line Items]
Weighted average amortization period (in years)	10 years
Trademarks & tradenames
Business Acquisition [Line Items]
Intangible assets	$ 7,000
Trademarks & tradenames | Buffalo Filter LLC
Business Acquisition [Line Items]
Weighted average amortization period (in years)	20 years
Pro Forma | Cost of Sales
Business Acquisition [Line Items]
Business acquisition costs			500		1,200
Pro Forma | Acquisition-related Costs | Selling and Administrative Expenses
Business Acquisition [Line Items]
Business acquisition costs			$ 2,500		$ 9,700