Condensed consolidating guarantor financial information - Income and Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 01, 2018	Jul. 02, 2017	Jul. 01, 2018	Jul. 02, 2017
Condensed Income Statements, Captions [Line Items]
Net revenues	$ 609,866	$ 528,613	$ 1,197,096	$ 1,016,494
Cost of goods sold	265,088	238,329	521,048	470,650
Gross profit	344,778	290,284	676,048	545,844
Selling, general and administrative expenses	229,917	158,934	445,254	322,903
Research and development expenses	26,018	20,278	52,045	38,105
Restructuring and impairment charges	55,353	870	58,416	13,815
Income from continuing operations before interest, loss on extinguishment of debt and taxes	33,490	110,202	120,333	171,021
Interest, net	26,466	19,733	52,136	37,290
Loss on extinguishment of debt	0	11	0	5,593
Income from continuing operations before taxes	7,024	90,458	68,197	128,138
(Benefit) taxes on (loss) income from continuing operations	9,576	12,095	15,818	9,426
Equity in net income of consolidated subsidiaries	0	0	0	0
Income from continuing operations	(2,552)	78,363	52,379	118,712
Operating loss from discontinued operations	94	(566)	1,329	(848)
Benefit on loss from discontinued operations	38	(206)	20	(309)
Income (loss) from discontinued operations	56	(360)	1,309	(539)
Net income	(2,496)	78,003	53,688	118,173
Other comprehensive income	(124,019)	69,822	(41,329)	119,422
Comprehensive income	(126,515)	147,825	12,359	237,595
Eliminations
Condensed Income Statements, Captions [Line Items]
Net revenues	(107,717)	(106,984)	(219,915)	(211,061)
Cost of goods sold	(109,931)	(104,313)	(213,583)	(207,889)
Gross profit	2,214	(2,671)	(6,332)	(3,172)
Selling, general and administrative expenses	199	(39)	(330)	524
Research and development expenses	0	0	0	0
Restructuring and impairment charges	0	0	0	0
Income from continuing operations before interest, loss on extinguishment of debt and taxes	2,015	(2,632)	(6,002)	(3,696)
Interest, net	0	0	0	0
Loss on extinguishment of debt		0		0
Income from continuing operations before taxes	2,015	(2,632)	(6,002)	(3,696)
(Benefit) taxes on (loss) income from continuing operations	63	(1,123)	(1,103)	(599)
Equity in net income of consolidated subsidiaries	(46,736)	(158,062)	(198,472)	(283,705)
Income from continuing operations	(44,784)	(159,571)	(203,371)	(286,802)
Operating loss from discontinued operations	0	0	0	0
Benefit on loss from discontinued operations	0	0	0	0
Income (loss) from discontinued operations	0	0	0	0
Net income	(44,784)	(159,571)	(203,371)	(286,802)
Other comprehensive income	245,642	(137,501)	88,296	(240,806)
Comprehensive income	200,858	(297,072)	(115,075)	(527,608)
Parent Company
Condensed Income Statements, Captions [Line Items]
Net revenues	0	0	0	0
Cost of goods sold	0	0	0	0
Gross profit	0	0	0	0
Selling, general and administrative expenses	12,430	7,468	21,611	27,987
Research and development expenses	489	264	716	499
Restructuring and impairment charges	0	0	0	0
Income from continuing operations before interest, loss on extinguishment of debt and taxes	(12,919)	(7,732)	(22,327)	(28,486)
Interest, net	24,788	27,233	46,929	51,506
Loss on extinguishment of debt		11		5,593
Income from continuing operations before taxes	(37,707)	(34,976)	(69,256)	(85,585)
(Benefit) taxes on (loss) income from continuing operations	(13,218)	(14,378)	(26,410)	(35,711)
Equity in net income of consolidated subsidiaries	21,937	98,961	96,504	168,586
Income from continuing operations	(2,552)	78,363	53,658	118,712
Operating loss from discontinued operations	94	(566)	50	(848)
Benefit on loss from discontinued operations	38	(206)	20	(309)
Income (loss) from discontinued operations	56	(360)	30	(539)
Net income	(2,496)	78,003	53,688	118,173
Other comprehensive income	(124,019)	69,822	(41,329)	119,422
Comprehensive income	(126,515)	147,825	12,359	237,595
Guarantor Subsidiaries
Condensed Income Statements, Captions [Line Items]
Net revenues	391,304	338,620	770,723	654,263
Cost of goods sold	231,487	190,202	449,091	382,203
Gross profit	159,817	148,418	321,632	272,060
Selling, general and administrative expenses	139,565	95,171	270,479	189,214
Research and development expenses	18,818	13,594	38,186	24,780
Restructuring and impairment charges	2,545	1,335	3,453	6,709
Income from continuing operations before interest, loss on extinguishment of debt and taxes	(1,111)	38,318	9,514	51,357
Interest, net	1,078	(8,581)	4,009	(16,143)
Loss on extinguishment of debt		0		0
Income from continuing operations before taxes	(2,189)	46,899	5,505	67,500
(Benefit) taxes on (loss) income from continuing operations	7,486	13,386	13,909	19,297
Equity in net income of consolidated subsidiaries	24,457	58,861	101,333	114,663
Income from continuing operations	14,782	92,374	92,929	162,866
Operating loss from discontinued operations	0	0	0	0
Benefit on loss from discontinued operations	0	0	0	0
Income (loss) from discontinued operations	0	0	0	0
Net income	14,782	92,374	92,929	162,866
Other comprehensive income	(114,917)	68,127	(44,798)	117,531
Comprehensive income	(100,135)	160,501	48,131	280,397
Non-Guarantor Subsidiaries
Condensed Income Statements, Captions [Line Items]
Net revenues	326,279	296,977	646,288	573,292
Cost of goods sold	143,532	152,440	285,540	296,336
Gross profit	182,747	144,537	360,748	276,956
Selling, general and administrative expenses	77,723	56,334	153,494	105,178
Research and development expenses	6,711	6,420	13,143	12,826
Restructuring and impairment charges	52,808	(465)	54,963	7,106
Income from continuing operations before interest, loss on extinguishment of debt and taxes	45,505	82,248	139,148	151,846
Interest, net	600	1,081	1,198	1,927
Loss on extinguishment of debt		0		0
Income from continuing operations before taxes	44,905	81,167	137,950	149,919
(Benefit) taxes on (loss) income from continuing operations	15,245	14,210	29,422	26,439
Equity in net income of consolidated subsidiaries	342	240	635	456
Income from continuing operations	30,002	67,197	109,163	123,936
Operating loss from discontinued operations	0	0	1,279	0
Benefit on loss from discontinued operations	0	0	0	0
Income (loss) from discontinued operations	0	0	1,279	0
Net income	30,002	67,197	110,442	123,936
Other comprehensive income	(130,725)	69,374	(43,498)	123,275
Comprehensive income	$ (100,723)	$ 136,571	$ 66,944	$ 247,211