Employer Sponsored Benefit Plans - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Aug. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Contributions made by company to domestic pension plan	$ 3,000	$ 1,200	$ 7,200	$ 3,600
Cost of sales	162,747	139,987	465,186	396,528
Selling, product development and administrative expenses	25,406	24,700	74,755	73,339
Accounting Standards Update 2017-07
Defined Benefit Plan Disclosure [Line Items]
Cost of sales		100		200
Selling, product development and administrative expenses		$ 100		$ 400
Interface
Defined Benefit Plan Disclosure [Line Items]
(Unfunded) Funded status of plan - asset (liability)					$ 11,200
Expected employer contributions during remainder of fiscal year	$ 300		$ 300
Post-retirement benefit plan | Interface
Defined Benefit Plan Disclosure [Line Items]
Benefit plan liabilities					4,100
Pension plan | Interface
Defined Benefit Plan Disclosure [Line Items]
Benefit plan liabilities					$ 2,900