Condensed consolidating guarantor financial information - Balance Sheets (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Apr. 01, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 271,212	$ 357,161	$ 378,872	$ 333,558
Accounts receivable, net of allowances of $9,225 and $9,348, respectively	375,756	366,286
Accounts receivable from consolidated subsidiaries	0	0
Inventories, net	445,566	427,778
Prepaid expenses and other current assets	79,595	72,481
Prepaid taxes	10,485	12,463
Total current assets	1,182,614	1,236,169
Property, plant and equipment, net	409,963	432,766
Operating lease assets	112,278
Goodwill	2,247,768	2,246,579
Intangible assets, net	2,274,488	2,325,052
Investments in affiliates	0	0
Deferred tax assets	2,500	2,446
Notes receivable and other amounts due from consolidated subsidiaries	0	0
Other assets	38,458	34,979
Total assets	6,268,069	6,277,991
Current liabilities
Current borrowings	86,625	86,625
Accounts payable	103,532	106,709
Accounts payable to consolidated subsidiaries	0	0
Accrued expenses	93,649	97,551
Current portion of contingent consideration	99,686	136,877
Payroll and benefit-related liabilities	76,261	104,670
Accrued interest	23,245	6,031
Income taxes payable	6,641	5,943
Other current liabilities	31,277	38,050
Total current liabilities	520,916	582,456
Long-term borrowings	2,072,939	2,072,200
Deferred tax liabilities	610,606	608,221
Pension and postretirement benefit liabilities	89,287	92,914
Noncurrent liability for uncertain tax positions	10,833	10,718
Notes payable and other amounts due to consolidated subsidiaries	0	0
Noncurrent contingent consideration	80,676	167,370
Noncurrent operating lease liabilities	100,708
Other liabilities	212,226	204,134
Total liabilities	3,698,191	3,738,013
Total shareholders' equity	2,569,878	2,539,978
Total liabilities and shareholders' equity	6,268,069	6,277,991
Eliminations
Current assets
Cash and cash equivalents	0	0
Accounts receivable, net of allowances of $9,225 and $9,348, respectively	4,976	5,334
Accounts receivable from consolidated subsidiaries	(652,056)	(1,425,771)
Inventories, net	(40,253)	(30,954)
Prepaid expenses and other current assets	4,113	4,113
Prepaid taxes	0	0
Total current assets	(683,220)	(1,447,278)
Property, plant and equipment, net	0	0
Operating lease assets	0
Goodwill	0	0
Intangible assets, net	0	0
Investments in affiliates	(7,814,988)	(7,677,731)
Deferred tax assets	(2,385)	(2,376)
Notes receivable and other amounts due from consolidated subsidiaries	(4,982,955)	(4,874,135)
Other assets	0	0
Total assets	(13,483,548)	(14,001,520)
Current liabilities
Current borrowings	0	0
Accounts payable	0	0
Accounts payable to consolidated subsidiaries	(652,056)	(1,425,771)
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	(1,435)	0
Other current liabilities	0	0
Total current liabilities	(653,491)	(1,425,771)
Long-term borrowings	0	0
Deferred tax liabilities	(2,385)	(2,376)
Pension and postretirement benefit liabilities	0	0
Noncurrent liability for uncertain tax positions	0	0
Notes payable and other amounts due to consolidated subsidiaries	(4,982,955)	(4,874,135)
Noncurrent contingent consideration	0	0
Noncurrent operating lease liabilities	0
Other liabilities	0
Total liabilities	(5,638,831)	(6,302,282)
Total shareholders' equity	(7,844,717)	(7,699,238)
Total liabilities and shareholders' equity	(13,483,548)	(14,001,520)
Parent Company
Current assets
Cash and cash equivalents	39,022	49,523	28,407	37,803
Accounts receivable, net of allowances of $9,225 and $9,348, respectively	4,286	5,885
Accounts receivable from consolidated subsidiaries	35,052	32,036
Inventories, net	0	0
Prepaid expenses and other current assets	38,633	30,458
Prepaid taxes	4,631	7,029
Total current assets	121,624	124,931
Property, plant and equipment, net	3,167	3,385
Operating lease assets	14,679
Goodwill	0	0
Intangible assets, net	85	90
Investments in affiliates	6,043,371	5,984,566
Deferred tax assets	0	0
Notes receivable and other amounts due from consolidated subsidiaries	1,976,376	2,337,737
Other assets	16,956	17,180
Total assets	8,176,258	8,467,889
Current liabilities
Current borrowings	36,625	36,625
Accounts payable	3,446	3,448
Accounts payable to consolidated subsidiaries	235,100	1,058,008
Accrued expenses	8,034	5,659
Current portion of contingent consideration	0	0
Payroll and benefit-related liabilities	14,092	17,156
Accrued interest	23,200	5,995
Income taxes payable	0	0
Other current liabilities	4,414	843
Total current liabilities	324,911	1,127,734
Long-term borrowings	2,072,939	2,072,200
Deferred tax liabilities	90,195	87,671
Pension and postretirement benefit liabilities	46,154	49,290
Noncurrent liability for uncertain tax positions	912	801
Notes payable and other amounts due to consolidated subsidiaries	2,920,820	2,451,784
Noncurrent contingent consideration	0	0
Noncurrent operating lease liabilities	12,218
Other liabilities	138,231	138,431
Total liabilities	5,606,380	5,927,911
Total shareholders' equity	2,569,878	2,539,978
Total liabilities and shareholders' equity	8,176,258	8,467,889
Guarantor Subsidiaries
Current assets
Cash and cash equivalents	622	1,757	10,200	8,933
Accounts receivable, net of allowances of $9,225 and $9,348, respectively	62,457	54,013
Accounts receivable from consolidated subsidiaries	228,267	1,043,573
Inventories, net	274,038	266,073
Prepaid expenses and other current assets	10,243	9,673
Prepaid taxes	0	0
Total current assets	575,627	1,375,089
Property, plant and equipment, net	230,983	253,037
Operating lease assets	62,027
Goodwill	1,255,350	1,254,848
Intangible assets, net	1,255,965	1,277,462
Investments in affiliates	1,771,617	1,672,908
Deferred tax assets	0	0
Notes receivable and other amounts due from consolidated subsidiaries	2,722,166	2,523,156
Other assets	11,593	5,776
Total assets	7,885,328	8,362,276
Current liabilities
Current borrowings	0	0
Accounts payable	61,327	62,764
Accounts payable to consolidated subsidiaries	315,782	278,715
Accrued expenses	34,673	41,883
Current portion of contingent consideration	98,622	106,514
Payroll and benefit-related liabilities	19,557	44,982
Accrued interest	0	0
Income taxes payable	0	0
Other current liabilities	14,425	34,916
Total current liabilities	544,386	569,774
Long-term borrowings	0	0
Deferred tax liabilities	258,470	257,522
Pension and postretirement benefit liabilities	27,162	27,454
Noncurrent liability for uncertain tax positions	7,267	7,212
Notes payable and other amounts due to consolidated subsidiaries	1,879,068	2,222,580
Noncurrent contingent consideration	42,717	131,563
Noncurrent operating lease liabilities	61,390
Other liabilities	9,497	8,204
Total liabilities	2,829,957	3,224,309
Total shareholders' equity	5,055,371	5,137,967
Total liabilities and shareholders' equity	7,885,328	8,362,276
Non-Guarantor Subsidiaries
Current assets
Cash and cash equivalents	231,568	305,881	$ 340,265	$ 286,822
Accounts receivable, net of allowances of $9,225 and $9,348, respectively	304,037	301,054
Accounts receivable from consolidated subsidiaries	388,737	350,162
Inventories, net	211,781	192,659
Prepaid expenses and other current assets	26,606	28,237
Prepaid taxes	5,854	5,434
Total current assets	1,168,583	1,183,427
Property, plant and equipment, net	175,813	176,344
Operating lease assets	35,572
Goodwill	992,418	991,731
Intangible assets, net	1,018,438	1,047,500
Investments in affiliates	0	20,257
Deferred tax assets	4,885	4,822
Notes receivable and other amounts due from consolidated subsidiaries	284,413	13,242
Other assets	9,909	12,023
Total assets	3,690,031	3,449,346
Current liabilities
Current borrowings	50,000	50,000
Accounts payable	38,759	40,497
Accounts payable to consolidated subsidiaries	101,174	89,048
Accrued expenses	50,942	50,009
Current portion of contingent consideration	1,064	30,363
Payroll and benefit-related liabilities	42,612	42,532
Accrued interest	45	36
Income taxes payable	8,076	5,943
Other current liabilities	12,438	2,291
Total current liabilities	305,110	310,719
Long-term borrowings	0	0
Deferred tax liabilities	264,326	265,404
Pension and postretirement benefit liabilities	15,971	16,170
Noncurrent liability for uncertain tax positions	2,654	2,705
Notes payable and other amounts due to consolidated subsidiaries	183,067	199,771
Noncurrent contingent consideration	37,959	35,807
Noncurrent operating lease liabilities	27,100
Other liabilities	64,498	57,499
Total liabilities	900,685	888,075
Total shareholders' equity	2,789,346	2,561,271
Total liabilities and shareholders' equity	$ 3,690,031	$ 3,449,346