Segment Information - Reconciliation of Reportable Segment Operating Income (Loss) to Corresponding Consolidated Amounts (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Amortization of acquired intangible assets			$ 11,100	$ 8,400
Restructuring Charges	$ 49	$ 860	49	1,835
Total operating income (loss)	23,819	14,801	44,659	27,963
Operating Segments
Segment Reporting Information [Line Items]
Total operating income (loss)	33,519	21,293	59,741	38,776
Segment Reconciling Items
Segment Reporting Information [Line Items]
Amortization of acquired intangible assets	4,629	3,294	9,218	6,358
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Other unallocated corporate expenses	$ 5,022	$ 2,338	$ 5,815	$ 2,620