Business Segments (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2018 USD ($) segment	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Sep. 30, 2017 USD ($)
Segment Reporting [Abstract]
Number of reportable segments			3	3
Segment Reporting Information [Line Items]
Revenue from product sales and services	$ 342,475	$ 311,142			$ 973,215	$ 890,916
Sales to external customers	342,475	311,142			973,215	890,916
Earnings before interest, taxes, depreciation and amortization (EBITDA)	36,400	44,716			112,398	88,675
Depreciation and amortization	21,562	18,293			61,924	55,813
Operating profit (loss)	14,838	26,424			50,475	32,862
Interest expense	(12,370)	(12,466)			(40,423)	(39,117)
Income (loss) before income taxes	2,468	13,958			10,052	(6,255)
Income tax (expense) benefit	(1,433)	(12,202)			960	(295)
Net income (loss)	1,035	1,756			11,012	(6,550)
Capital expenditures	22,899	13,247			54,569	40,475
Assets	1,499,221		$ 1,499,221	$ 1,499,221	1,499,221		$ 1,473,309
Goodwill	324,272		324,272	324,272	324,272		321,913
Industrial [Member]
Segment Reporting Information [Line Items]
Capital expenditures	14,364	9,256			34,866	31,019
Municipal [Member]
Segment Reporting Information [Line Items]
Capital expenditures	3,182	561			6,154	1,577
Product [Member]
Segment Reporting Information [Line Items]
Capital expenditures	2,817	1,658			5,138	4,239
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from product sales and services	21,598	17,836			59,400	49,576
Intersegment Eliminations [Member] | Industrial [Member]
Segment Reporting Information [Line Items]
Revenue from product sales and services	1,810	1,206			7,575	3,553
Intersegment Eliminations [Member] | Municipal [Member]
Segment Reporting Information [Line Items]
Revenue from product sales and services	7,428	7,075			21,079	18,970
Intersegment Eliminations [Member] | Product [Member]
Segment Reporting Information [Line Items]
Revenue from product sales and services	12,360	9,555			30,746	27,053
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue from product sales and services	364,073	328,978			1,032,615	940,492
Operating Segments [Member] | Industrial [Member]
Segment Reporting Information [Line Items]
Revenue from product sales and services	184,133	155,904			536,351	464,414
Sales to external customers	182,323	154,698			528,776	460,861
Earnings before interest, taxes, depreciation and amortization (EBITDA)	35,805	34,758			117,646	102,133
Depreciation and amortization	11,390	9,191			32,244	27,632
Operating profit (loss)	24,415	25,567			85,402	74,501
Assets	492,875		492,875	492,875	492,875		461,471
Goodwill	127,357		127,357	127,357	127,357		128,190
Operating Segments [Member] | Municipal [Member]
Segment Reporting Information [Line Items]
Revenue from product sales and services	75,927	79,817			215,768	217,897
Sales to external customers	68,499	72,742			194,689	198,927
Earnings before interest, taxes, depreciation and amortization (EBITDA)	14,434	12,556			30,784	29,644
Depreciation and amortization	1,736	1,994			5,312	6,119
Operating profit (loss)	12,698	10,562			25,472	23,525
Assets	171,438		171,438	171,438	171,438		155,698
Goodwill	9,741		9,741	9,741	9,741		9,865
Operating Segments [Member] | Product [Member]
Segment Reporting Information [Line Items]
Revenue from product sales and services	104,013	93,257			280,496	258,181
Sales to external customers	91,653	83,702			249,750	231,128
Earnings before interest, taxes, depreciation and amortization (EBITDA)	23,989	21,196			57,635	53,070
Depreciation and amortization	3,269	2,084			9,345	8,722
Operating profit (loss)	20,720	19,112			48,290	44,348
Assets	538,430		538,430	538,430	538,430		513,941
Goodwill	187,174		187,174	187,174	187,174		183,858
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Earnings before interest, taxes, depreciation and amortization (EBITDA)	(37,828)	(23,794)			(93,667)	(96,172)
Depreciation and amortization	5,167	5,024			15,023	13,340
Operating profit (loss)	(42,995)	(28,817)			(108,689)	(109,512)
Capital expenditures	2,536	$ 1,772			8,411	$ 3,640
Assets	$ 296,478		$ 296,478	$ 296,478	$ 296,478		$ 342,199