Condensed consolidating guarantor financial information - Income and Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2018
Condensed Income Statements, Captions [Line Items]
Net revenues	$ 613,584	$ 587,230
Cost of goods sold	268,842	255,960
Gross profit	344,742	331,270
Selling, general and administrative expenses	227,693	215,337
Research and development expenses	27,150	26,027
Restructuring and impairment charges	17,395	3,063
Gain on sale of assets	(2,739)	0
Income from continuing operations before interest and taxes	75,243	86,843
Interest, net	22,353	25,670
Income from continuing operations before taxes	52,890	61,173
(Benefit) taxes on (loss) income from continuing operations	10,972	6,242
Equity in net income of consolidated subsidiaries	0	0
Income from continuing operations	41,918	54,931
Operating loss from discontinued operations	(1,343)	1,235
Benefit on loss from discontinued operations	(322)	(18)
Income (loss) from discontinued operations	(1,021)	1,253
Net income	40,897	56,184
Other comprehensive income	396	82,690
Comprehensive income	41,293	138,874
Eliminations
Condensed Income Statements, Captions [Line Items]
Net revenues	(122,552)	(112,198)
Cost of goods sold	(113,232)	(103,652)
Gross profit	(9,320)	(8,546)
Selling, general and administrative expenses	358	(529)
Research and development expenses	0	0
Restructuring and impairment charges	0	0
Gain on sale of assets	0
Income from continuing operations before interest and taxes	(9,678)	(8,017)
Interest, net	0	0
Income from continuing operations before taxes	(9,678)	(8,017)
(Benefit) taxes on (loss) income from continuing operations	(1,435)	(1,166)
Equity in net income of consolidated subsidiaries	(113,393)	(151,736)
Income from continuing operations	(121,636)	(158,587)
Operating loss from discontinued operations	0	0
Benefit on loss from discontinued operations	0	0
Income (loss) from discontinued operations	0	0
Net income	(121,636)	(158,587)
Other comprehensive income	6,495	(157,346)
Comprehensive income	(115,141)	(315,933)
Parent Company
Condensed Income Statements, Captions [Line Items]
Net revenues	0	0
Cost of goods sold	0	0
Gross profit	0	0
Selling, general and administrative expenses	16,167	9,181
Research and development expenses	484	227
Restructuring and impairment charges	0	0
Gain on sale of assets	0
Income from continuing operations before interest and taxes	(16,651)	(9,408)
Interest, net	4,065	22,141
Income from continuing operations before taxes	(20,716)	(31,549)
(Benefit) taxes on (loss) income from continuing operations	(8,872)	(13,192)
Equity in net income of consolidated subsidiaries	53,762	74,567
Income from continuing operations	41,918	56,210
Operating loss from discontinued operations	(1,343)	(44)
Benefit on loss from discontinued operations	(322)	(18)
Income (loss) from discontinued operations	(1,021)	(26)
Net income	40,897	56,184
Other comprehensive income	396	82,690
Comprehensive income	41,293	138,874
Guarantor Subsidiaries
Condensed Income Statements, Captions [Line Items]
Net revenues	415,143	379,419
Cost of goods sold	234,217	217,604
Gross profit	180,926	161,815
Selling, general and administrative expenses	131,702	130,914
Research and development expenses	20,121	19,368
Restructuring and impairment charges	5,973	908
Gain on sale of assets	0
Income from continuing operations before interest and taxes	23,130	10,625
Interest, net	18,597	2,931
Income from continuing operations before taxes	4,533	7,694
(Benefit) taxes on (loss) income from continuing operations	6,892	6,423
Equity in net income of consolidated subsidiaries	59,631	76,876
Income from continuing operations	57,272	78,147
Operating loss from discontinued operations	0	0
Benefit on loss from discontinued operations	0	0
Income (loss) from discontinued operations	0	0
Net income	57,272	78,147
Other comprehensive income	(1,501)	70,119
Comprehensive income	55,771	148,266
Non-Guarantor Subsidiaries
Condensed Income Statements, Captions [Line Items]
Net revenues	320,993	320,009
Cost of goods sold	147,857	142,008
Gross profit	173,136	178,001
Selling, general and administrative expenses	79,466	75,771
Research and development expenses	6,545	6,432
Restructuring and impairment charges	11,422	2,155
Gain on sale of assets	(2,739)
Income from continuing operations before interest and taxes	78,442	93,643
Interest, net	(309)	598
Income from continuing operations before taxes	78,751	93,045
(Benefit) taxes on (loss) income from continuing operations	14,387	14,177
Equity in net income of consolidated subsidiaries	0	293
Income from continuing operations	64,364	79,161
Operating loss from discontinued operations	0	1,279
Benefit on loss from discontinued operations	0	0
Income (loss) from discontinued operations	0	1,279
Net income	64,364	80,440
Other comprehensive income	(4,994)	87,227
Comprehensive income	$ 59,370	$ 167,667