Segment Information - Performance of Segments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Sep. 30, 2016
Segment Reporting Information [Line Items]
Net revenue	$ 372,345	$ 353,963	$ 1,094,138	$ 1,045,393
EBITDA	39,285	36,263	108,911	100,066
Total assets	1,081,105		1,081,105		$ 1,086,158
Depreciation and amortization	19,161	18,634	56,146	54,952
Purchases of property and equipment	12,186	12,636	32,981	31,655
Operating Segments | I/DD
Segment Reporting Information [Line Items]
Net revenue	243,496	233,836	719,207	694,351
EBITDA	34,098	34,161	99,971	102,114
Total assets	469,612		469,612
Depreciation and amortization	9,451	9,717	27,988	28,638
Purchases of property and equipment	7,093	5,444	18,390	15,327
Operating Segments | SRS
Segment Reporting Information [Line Items]
Net revenue	77,758	73,506	229,301	213,549
EBITDA	13,778	14,391	40,670	40,471
Total assets	261,129		261,129
Depreciation and amortization	5,858	5,827	17,483	17,639
Purchases of property and equipment	2,865	2,497	8,016	7,774
Operating Segments | ARY
Segment Reporting Information [Line Items]
Net revenue	35,368	35,364	106,784	113,279
EBITDA	5,786	5,993	16,614	15,883
Total assets	85,393		85,393
Depreciation and amortization	1,407	1,433	4,255	4,407
Purchases of property and equipment	329	692	961	1,508
Corporate and Other
Segment Reporting Information [Line Items]
Net revenue	15,723	11,257	38,846	24,214
EBITDA	(14,377)	(18,282)	(48,344)	(58,402)
Total assets	264,971		264,971
Depreciation and amortization	2,445	1,657	6,420	4,268
Purchases of property and equipment	$ 1,899	$ 4,003	$ 5,614	$ 7,046