Segment Reporting (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Mar. 31, 2018 USD ($) reportable_segment	Mar. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)
Segment Reporting [Line Items]
Number of reportable segments | reportable_segment			3
Net sales	$ 390,183	$ 364,599	$ 753,274	$ 703,970
Income (loss) from operations	33,196	32,198	57,768	58,454
Capital expenditures			2,909	4,209
Depreciation and amortization			14,541	13,472
Total assets	1,812,312		1,812,312		$ 1,754,107
Goodwill	266,644		266,644		266,644
Unallocated Corporate Costs
Segment Reporting [Line Items]
Net sales	0	0	0	0
Income (loss) from operations	(10,102)	(4,282)	(17,377)	(9,208)
Interest expense, net	0	0	0	0
Capital expenditures	0	0	0	0
Depreciation and amortization	0	0	0	0
Consolidated
Segment Reporting [Line Items]
Net sales	390,183	364,599	753,274	703,970
Income (loss) from operations	33,196	32,198	57,768	58,454
Interest expense, net	(11,965)	(8,842)	(23,803)	(19,915)
Capital expenditures	1,574	2,893	2,909	4,209
Depreciation and amortization	7,285	6,743	14,541	13,472
Total assets	1,812,312		1,812,312		1,754,107
Goodwill	266,644		266,644		266,644
Americas | Operating segments
Segment Reporting [Line Items]
Net sales	313,250	293,025	602,765	560,963
Income (loss) from operations	35,691	27,076	60,888	49,103
Interest expense, net	(10,943)	(8,091)	(21,591)	(18,208)
Capital expenditures	1,412	2,346	2,370	3,383
Depreciation and amortization	6,283	5,914	12,659	11,848
Total assets	1,498,308		1,498,308		1,436,840
Goodwill	204,183		204,183		204,183
EMEA | Operating segments
Segment Reporting [Line Items]
Net sales	68,147	64,434	132,385	128,339
Income (loss) from operations	6,830	7,956	11,982	16,675
Interest expense, net	(997)	(729)	(2,161)	(1,659)
Capital expenditures	75	544	400	812
Depreciation and amortization	929	806	1,735	1,584
Total assets	263,999		263,999		275,445
Goodwill	51,190		51,190		51,190
APAC | Operating segments
Segment Reporting [Line Items]
Net sales	8,786	7,140	18,124	14,668
Income (loss) from operations	777	1,448	2,275	1,884
Interest expense, net	(25)	(22)	(51)	(48)
Capital expenditures	87	3	139	14
Depreciation and amortization	73	$ 23	147	$ 40
Total assets	50,005		50,005		41,822
Goodwill	$ 11,271		$ 11,271		$ 11,271