Condensed consolidating guarantor financial information - Balance Sheets (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Oct. 01, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents	$ 356,276	$ 333,558	$ 1,017,573	$ 543,789
Accounts receivable, net	374,341	345,875
Accounts receivable from consolidated subsidiaries	0	0
Inventories, net	411,066	395,744
Prepaid expenses and other current assets	55,173	47,882
Prepaid taxes	40,715	5,748
Assets held for sale	3,239	0
Total current assets	1,240,810	1,128,807
Property, plant and equipment, net	421,265	382,999
Goodwill	2,223,429	2,235,592
Intangible assets, net	2,262,818	2,383,748
Investments in consolidated subsidiaries	0	0
Deferred tax assets	2,305	3,810
Notes receivable and other amounts due from consolidated subsidiaries	0	0
Other assets	50,093	46,536
Total assets	6,200,720	6,181,492
Current liabilities
Current borrowings	77,250	86,625
Accounts payable	97,628	92,027
Accounts payable to consolidated subsidiaries	0	0
Accrued expenses	105,584	96,853
Current portion of contingent consideration	102,664	74,224
Payroll and benefit-related liabilities	94,132	107,415
Accrued interest	20,623	6,165
Income taxes payable	13,347	11,514
Other current liabilities	38,065	9,053
Total current liabilities	549,293	483,876
Long-term borrowings	2,075,834	2,162,927
Deferred tax liabilities	606,082	603,676
Pension and postretirement benefit liabilities	99,350	121,410
Noncurrent liability for uncertain tax positions	13,170	12,296
Notes payable and other amounts due to consolidated subsidiaries	0	0
Noncurrent contingent consideration	141,910	197,912
Other liabilities	208,016	168,864
Total liabilities	3,693,655	3,750,961
Total shareholders' equity	2,507,065	2,430,531
Total liabilities and shareholders' equity	6,200,720	6,181,492
Eliminations
Current assets
Cash and cash equivalents	0	0	0	0
Accounts receivable, net	5,015	4,663
Accounts receivable from consolidated subsidiaries	(1,370,582)	(1,534,839)
Inventories, net	(32,318)	(26,279)
Prepaid expenses and other current assets	3,982	3,982
Prepaid taxes	0	0
Assets held for sale	0
Total current assets	(1,393,903)	(1,552,473)
Property, plant and equipment, net	0	0
Goodwill	0	0
Intangible assets, net	0	0
Investments in consolidated subsidiaries	(7,623,587)	(7,499,941)
Deferred tax assets	(2,284)	(2,261)
Notes receivable and other amounts due from consolidated subsidiaries	(4,710,847)	(4,683,933)
Other assets	0	0
Total assets	(13,730,621)	(13,738,608)
Current liabilities
Current borrowings	0	0
Accounts payable	0	0
Accounts payable to consolidated subsidiaries	(1,370,582)	(1,534,839)
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	(1,090)	0
Other current liabilities	0	0
Total current liabilities	(1,371,672)	(1,534,839)
Long-term borrowings	0	0
Deferred tax liabilities	(2,284)	(2,261)
Pension and postretirement benefit liabilities	0	0
Noncurrent liability for uncertain tax positions	0	0
Notes payable and other amounts due to consolidated subsidiaries	(4,710,847)	(4,683,933)
Noncurrent contingent consideration	0	0
Other liabilities	0	0
Total liabilities	(6,084,803)	(6,221,033)
Total shareholders' equity	(7,645,818)	(7,517,575)
Total liabilities and shareholders' equity	(13,730,621)	(13,738,608)
Parent Company
Current assets
Cash and cash equivalents	47,766	37,803	45,189	14,571
Accounts receivable, net	2,932	2,414
Accounts receivable from consolidated subsidiaries	24,606	14,478
Inventories, net	0	0
Prepaid expenses and other current assets	14,379	14,874
Prepaid taxes	33,766	0
Assets held for sale	0
Total current assets	123,449	69,569
Property, plant and equipment, net	3,177	2,088
Goodwill	0	0
Intangible assets, net	95	0
Investments in consolidated subsidiaries	5,929,366	5,806,244
Deferred tax assets	0	0
Notes receivable and other amounts due from consolidated subsidiaries	2,265,457	2,452,101
Other assets	30,226	31,173
Total assets	8,351,770	8,361,175
Current liabilities
Current borrowings	27,250	36,625
Accounts payable	4,254	4,269
Accounts payable to consolidated subsidiaries	1,024,109	1,211,568
Accrued expenses	17,966	17,957
Current portion of contingent consideration	0	0
Payroll and benefit-related liabilities	18,184	21,145
Accrued interest	20,595	6,133
Income taxes payable	0	4,352
Other current liabilities	1,637	1,461
Total current liabilities	1,113,995	1,303,510
Long-term borrowings	2,075,834	2,162,927
Deferred tax liabilities	92,270	88,512
Pension and postretirement benefit liabilities	49,853	70,860
Noncurrent liability for uncertain tax positions	1,986	1,117
Notes payable and other amounts due to consolidated subsidiaries	2,370,469	2,155,146
Noncurrent contingent consideration	0	0
Other liabilities	140,298	148,572
Total liabilities	5,844,705	5,930,644
Total shareholders' equity	2,507,065	2,430,531
Total liabilities and shareholders' equity	8,351,770	8,361,175
Guarantor Subsidiaries
Current assets
Cash and cash equivalents	1,288	8,933	748,412	1,031
Accounts receivable, net	55,452	57,818
Accounts receivable from consolidated subsidiaries	994,236	1,177,246
Inventories, net	245,600	245,533
Prepaid expenses and other current assets	12,409	9,236
Prepaid taxes	0	0
Assets held for sale	3,239
Total current assets	1,312,224	1,498,766
Property, plant and equipment, net	238,079	213,663
Goodwill	1,245,455	1,246,144
Intangible assets, net	1,274,994	1,355,275
Investments in consolidated subsidiaries	1,673,596	1,674,077
Deferred tax assets	0	0
Notes receivable and other amounts due from consolidated subsidiaries	2,445,390	2,231,832
Other assets	6,057	6,397
Total assets	8,195,795	8,226,154
Current liabilities
Current borrowings	0	0
Accounts payable	54,791	46,992
Accounts payable to consolidated subsidiaries	280,381	261,121
Accrued expenses	36,206	31,827
Current portion of contingent consideration	101,573	74,224
Payroll and benefit-related liabilities	31,405	44,009
Accrued interest	0	0
Income taxes payable	0	0
Other current liabilities	33,589	3,775
Total current liabilities	537,945	461,948
Long-term borrowings	0	0
Deferred tax liabilities	264,288	265,426
Pension and postretirement benefit liabilities	32,019	32,750
Noncurrent liability for uncertain tax positions	8,352	8,196
Notes payable and other amounts due to consolidated subsidiaries	2,135,450	2,320,611
Noncurrent contingent consideration	131,578	186,923
Other liabilities	9,026	7,850
Total liabilities	3,118,658	3,283,704
Total shareholders' equity	5,077,137	4,942,450
Total liabilities and shareholders' equity	8,195,795	8,226,154
Non-Guarantor Subsidiaries
Current assets
Cash and cash equivalents	307,222	286,822	$ 223,972	$ 528,187
Accounts receivable, net	310,942	280,980
Accounts receivable from consolidated subsidiaries	351,740	343,115
Inventories, net	197,784	176,490
Prepaid expenses and other current assets	24,403	19,790
Prepaid taxes	6,949	5,748
Assets held for sale	0
Total current assets	1,199,040	1,112,945
Property, plant and equipment, net	180,009	167,248
Goodwill	977,974	989,448
Intangible assets, net	987,729	1,028,473
Investments in consolidated subsidiaries	20,625	19,620
Deferred tax assets	4,589	6,071
Notes receivable and other amounts due from consolidated subsidiaries	0	0
Other assets	13,810	8,966
Total assets	3,383,776	3,332,771
Current liabilities
Current borrowings	50,000	50,000
Accounts payable	38,583	40,766
Accounts payable to consolidated subsidiaries	66,092	62,150
Accrued expenses	51,412	47,069
Current portion of contingent consideration	1,091	0
Payroll and benefit-related liabilities	44,543	42,261
Accrued interest	28	32
Income taxes payable	14,437	7,162
Other current liabilities	2,839	3,817
Total current liabilities	269,025	253,257
Long-term borrowings	0	0
Deferred tax liabilities	251,808	251,999
Pension and postretirement benefit liabilities	17,478	17,800
Noncurrent liability for uncertain tax positions	2,832	2,983
Notes payable and other amounts due to consolidated subsidiaries	204,928	208,176
Noncurrent contingent consideration	10,332	10,989
Other liabilities	58,692	12,442
Total liabilities	815,095	757,646
Total shareholders' equity	2,568,681	2,575,125
Total liabilities and shareholders' equity	$ 3,383,776	$ 3,332,771