Condensed consolidating guarantor financial information - Balance Sheets (Details) - USD ($) $ in Thousands	Oct. 01, 2017	Dec. 31, 2016	Sep. 25, 2016	Dec. 31, 2015
Current assets
Cash and cash equivalents	$ 1,017,573	$ 543,789	$ 499,459	$ 338,366
Accounts receivable, net	306,472	271,993
Accounts receivable from consolidated subsidiaries	0	0
Inventories, net	382,417	316,171
Prepaid expenses and other current assets	51,599	40,382
Prepaid taxes	8,690	8,179
Assets held for sale	0	2,879
Total current assets	1,766,751	1,183,393
Property, plant and equipment, net	374,461	302,899
Goodwill	1,886,157	1,276,720
Intangible assets, net	1,606,943	1,091,663
Investments in consolidated subsidiaries	0	0
Deferred tax assets	2,020	1,712
Notes receivable and other amounts due from consolidated subsidiaries	0	0
Other assets	44,401	34,826
Total assets	5,680,733	3,891,213
Current liabilities
Current borrowings	77,250	183,071
Accounts payable	85,419	69,400
Accounts payable to consolidated subsidiaries	0	0
Accrued expenses	88,095	65,149
Current portion of contingent consideration	591	587
Payroll and benefit-related liabilities	88,091	82,679
Accrued interest	13,430	10,450
Income taxes payable	12,857	7,908
Other current liabilities	8,912	8,402
Total current liabilities	374,645	427,646
Long-term borrowings	2,172,805	850,252
Deferred tax liabilities	471,667	271,377
Pension and postretirement benefit liabilities	116,441	133,062
Noncurrent liability for uncertain tax positions	14,238	17,520
Notes payable and other amounts due to consolidated subsidiaries	0	0
Other liabilities	58,460	52,015
Total liabilities	3,208,256	1,751,872
Convertible notes - redeemable equity component	0	1,824
Mezzanine equity	0	1,824
Total shareholders' equity	2,472,477	2,137,517
Total liabilities and shareholders' equity	5,680,733	3,891,213
Eliminations
Current assets
Cash and cash equivalents	0	0	0	0
Accounts receivable, net	4,460	4,859
Accounts receivable from consolidated subsidiaries	(2,641,895)	(2,490,069)
Inventories, net	(28,499)	(25,087)
Prepaid expenses and other current assets	3,337	3,337
Prepaid taxes	0	413
Assets held for sale		0
Total current assets	(2,662,597)	(2,506,547)
Property, plant and equipment, net	0	0
Goodwill	0	0
Intangible assets, net	0	0
Investments in consolidated subsidiaries	(9,070,888)	(7,564,758)
Deferred tax assets	(3,476)	(76,524)
Notes receivable and other amounts due from consolidated subsidiaries	(4,338,574)	(3,473,153)
Other assets	0	0
Total assets	(16,075,535)	(13,620,982)
Current liabilities
Current borrowings	0	0
Accounts payable	0	0
Accounts payable to consolidated subsidiaries	(2,641,895)	(2,490,069)
Accrued expenses	0	0
Current portion of contingent consideration	0	0
Payroll and benefit-related liabilities	0	0
Accrued interest	0	0
Income taxes payable	(593)	85
Other current liabilities	0	0
Total current liabilities	(2,642,488)	(2,489,984)
Long-term borrowings	0	0
Deferred tax liabilities	(3,476)	(76,524)
Pension and postretirement benefit liabilities	0	0
Noncurrent liability for uncertain tax positions	0	0
Notes payable and other amounts due to consolidated subsidiaries	(4,338,574)	(3,473,153)
Other liabilities	0	0
Total liabilities	(6,984,538)	(6,039,661)
Convertible notes - redeemable equity component		0
Mezzanine equity		0
Total shareholders' equity	(9,090,997)	(7,581,321)
Total liabilities and shareholders' equity	(16,075,535)	(13,620,982)
Parent Company
Current assets
Cash and cash equivalents	45,189	14,571	33,460	21,612
Accounts receivable, net	2,232	2,551
Accounts receivable from consolidated subsidiaries	9,095	4,861
Inventories, net	0	0
Prepaid expenses and other current assets	15,492	14,239
Prepaid taxes	0	0
Assets held for sale		0
Total current assets	72,008	36,222
Property, plant and equipment, net	2,247	2,566
Goodwill	0	0
Intangible assets, net	0	0
Investments in consolidated subsidiaries	7,245,740	6,022,042
Deferred tax assets	0	73,051
Notes receivable and other amounts due from consolidated subsidiaries	2,082,206	1,387,615
Other assets	29,378	22,295
Total assets	9,431,579	7,543,791
Current liabilities
Current borrowings	27,250	133,071
Accounts payable	2,343	4,540
Accounts payable to consolidated subsidiaries	2,307,797	2,242,814
Accrued expenses	20,127	16,827
Current portion of contingent consideration	0	0
Payroll and benefit-related liabilities	19,973	20,610
Accrued interest	13,402	10,429
Income taxes payable	2,168	1,246
Other current liabilities	344	2,262
Total current liabilities	2,393,404	2,431,799
Long-term borrowings	2,172,805	850,252
Deferred tax liabilities	118,891	0
Pension and postretirement benefit liabilities	67,836	85,645
Noncurrent liability for uncertain tax positions	2,035	1,169
Notes payable and other amounts due to consolidated subsidiaries	2,178,181	2,011,737
Other liabilities	25,950	23,848
Total liabilities	6,959,102	5,404,450
Convertible notes - redeemable equity component		1,824
Mezzanine equity		1,824
Total shareholders' equity	2,472,477	2,137,517
Total liabilities and shareholders' equity	9,431,579	7,543,791
Guarantor Subsidiaries
Current assets
Cash and cash equivalents	748,412	1,031	1,024	0
Accounts receivable, net	36,055	8,768
Accounts receivable from consolidated subsidiaries	2,273,240	2,176,059
Inventories, net	236,355	200,852
Prepaid expenses and other current assets	8,722	5,332
Prepaid taxes	0	0
Assets held for sale		0
Total current assets	3,302,784	2,392,042
Property, plant and equipment, net	209,966	163,847
Goodwill	902,429	708,546
Intangible assets, net	612,745	640,999
Investments in consolidated subsidiaries	1,801,602	1,519,031
Deferred tax assets	0	0
Notes receivable and other amounts due from consolidated subsidiaries	2,256,368	2,085,538
Other assets	6,308	6,254
Total assets	9,092,202	7,516,257
Current liabilities
Current borrowings	0	0
Accounts payable	47,014	30,924
Accounts payable to consolidated subsidiaries	275,465	214,203
Accrued expenses	24,398	18,126
Current portion of contingent consideration	591	587
Payroll and benefit-related liabilities	28,011	26,672
Accrued interest	0	0
Income taxes payable	0	0
Other current liabilities	5,335	3,643
Total current liabilities	380,814	294,155
Long-term borrowings	0	0
Deferred tax liabilities	314,168	316,526
Pension and postretirement benefit liabilities	30,928	31,561
Noncurrent liability for uncertain tax positions	9,175	13,684
Notes payable and other amounts due to consolidated subsidiaries	1,954,051	1,264,004
Other liabilities	13,943	15,695
Total liabilities	2,703,079	1,935,625
Convertible notes - redeemable equity component		0
Mezzanine equity		0
Total shareholders' equity	6,389,123	5,580,632
Total liabilities and shareholders' equity	9,092,202	7,516,257
Non-Guarantor Subsidiaries
Current assets
Cash and cash equivalents	223,972	528,187	$ 464,975	$ 316,754
Accounts receivable, net	263,725	255,815
Accounts receivable from consolidated subsidiaries	359,560	309,149
Inventories, net	174,561	140,406
Prepaid expenses and other current assets	24,048	17,474
Prepaid taxes	8,690	7,766
Assets held for sale		2,879
Total current assets	1,054,556	1,261,676
Property, plant and equipment, net	162,248	136,486
Goodwill	983,728	568,174
Intangible assets, net	994,198	450,664
Investments in consolidated subsidiaries	23,546	23,685
Deferred tax assets	5,496	5,185
Notes receivable and other amounts due from consolidated subsidiaries	0	0
Other assets	8,715	6,277
Total assets	3,232,487	2,452,147
Current liabilities
Current borrowings	50,000	50,000
Accounts payable	36,062	33,936
Accounts payable to consolidated subsidiaries	58,633	33,052
Accrued expenses	43,570	30,196
Current portion of contingent consideration	0	0
Payroll and benefit-related liabilities	40,107	35,397
Accrued interest	28	21
Income taxes payable	11,282	6,577
Other current liabilities	3,233	2,497
Total current liabilities	242,915	191,676
Long-term borrowings	0	0
Deferred tax liabilities	42,084	31,375
Pension and postretirement benefit liabilities	17,677	15,856
Noncurrent liability for uncertain tax positions	3,028	2,667
Notes payable and other amounts due to consolidated subsidiaries	206,342	197,412
Other liabilities	18,567	12,472
Total liabilities	530,613	451,458
Convertible notes - redeemable equity component		0
Mezzanine equity		0
Total shareholders' equity	2,701,874	2,000,689
Total liabilities and shareholders' equity	$ 3,232,487	$ 2,452,147