Condensed Consolidating Financial Information - Statements of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016	Sep. 30, 2016
Cash flows from operating activities:
Net income	$ 5,132	$ 2,384	$ 11,960	$ 15,105
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization	18,365	14,115	36,207	27,897
Interest expense related to amortization of debt issue costs and debt discount	700	600	1,606	1,184
Debt pre-payment premiums			0	93
Stock-based compensation	400	800	901	1,521
Deferred income taxes			7,099	8,643
Tax benefit from exercise of stock appreciation rights and vesting of restricted stock			(5,860)	(97)
Net loss (gain) on disposition of property, plant and equipment			(216)	(46)
Net loss of unconsolidated joint venture			19	26
Equity in earnings of subsidiaries			0
Decrease (increase) in trade receivables			19,682	33,538
Increase in inventories			(14,958)	(4,066)
Decrease in accounts payable and accrued liabilities			(19,413)	(36,372)
Other changes in operating assets and liabilities, net			(2,357)	(2,985)
Net cash provided by (used in) operating activities			34,670	44,441
Cash flows from investing activities:
Business acquisitions, net of cash acquired			(10,530)	(96,457)
Purchase of property, plant and equipment	(14,193)	(13,197)	(29,733)	(20,882)
Proceeds from disposition of property, plant and equipment			626	404
Net decrease (increase) in long-term receivables and deposits			4,890	(1,729)
Net change in other assets			2,368	(3,817)
Net cash provided by (used in) investing activities			(32,379)	(122,481)
Cash flows from financing activities:
Payments on long-term debt			(15,000)	(5,874)
Debt pre-payment premiums			0	(93)
Dividends paid to non-controlling interest in consolidated subsidiary			(657)	(735)
Employee stock purchases			336	539
Tax benefit from exercise of stock appreciation rights and vesting of restricted stock			5,860	97
Intercompany transfers			0	0
Net cash provided by (used in) financing activities			(9,461)	(6,066)
Net increase (decrease) in cash and cash equivalents			(7,170)	(84,106)
Cash and cash equivalents, beginning of period			65,298	142,597	$ 142,597
Cash and cash equivalents, end of period	58,128	58,491	58,128	58,491	65,298
Consolidation, Eliminations
Cash flows from operating activities:
Net income	(15,928)	(11,021)	(33,493)	(29,647)
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Equity in earnings of subsidiaries	15,928	11,021	33,493	29,647
Guarantor Subsidiaries
Cash flows from operating activities:
Net income	14,282	10,582	31,606	28,773
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization			32,584	26,084
Stock-based compensation			327	537
Deferred income taxes			3,097	6,809
Tax benefit from exercise of stock appreciation rights and vesting of restricted stock				(95)
Net loss (gain) on disposition of property, plant and equipment			(223)	(49)
Decrease (increase) in trade receivables			19,370	34,198
Increase in inventories			(14,448)	(3,097)
Decrease in accounts payable and accrued liabilities			(15,864)	(17,680)
Other changes in operating assets and liabilities, net			(13,849)	(9,522)
Net cash provided by (used in) operating activities			42,600	65,958
Cash flows from investing activities:
Business acquisitions, net of cash acquired			(10,530)	(73,800)
Purchase of property, plant and equipment			(27,561)	(18,856)
Proceeds from disposition of property, plant and equipment			597	404
Net decrease (increase) in long-term receivables and deposits			1,731	(1,546)
Net change in other assets			(346)	(1,443)
Net cash provided by (used in) investing activities			(36,109)	(95,241)
Cash flows from financing activities:
Employee stock purchases			235	390
Tax benefit from exercise of stock appreciation rights and vesting of restricted stock				95
Intercompany transfers			(4,394)	18,968
Net cash provided by (used in) financing activities			(4,159)	19,453
Net increase (decrease) in cash and cash equivalents			2,332	(9,830)
Cash and cash equivalents, beginning of period			27,012	25,819	25,819
Cash and cash equivalents, end of period	29,344	15,989	29,344	15,989	27,012
Non-Guarantor Subsidiaries
Cash flows from operating activities:
Net income	2,237	722	2,639	1,453
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization			2,237	1,503
Deferred income taxes			465	159
Net loss (gain) on disposition of property, plant and equipment			7	3
Net loss of unconsolidated joint venture			19	26
Decrease (increase) in trade receivables			312	(660)
Increase in inventories			(510)	(969)
Decrease in accounts payable and accrued liabilities			(2,087)	(3,178)
Other changes in operating assets and liabilities, net			870	3,109
Net cash provided by (used in) operating activities			3,952	1,446
Cash flows from investing activities:
Business acquisitions, net of cash acquired				(22,657)
Purchase of property, plant and equipment			(673)	(268)
Proceeds from disposition of property, plant and equipment			29
Net decrease (increase) in long-term receivables and deposits			(8)	(22)
Net change in other assets			2,207	(109)
Net cash provided by (used in) investing activities			1,555	(23,056)
Cash flows from financing activities:
Dividends paid to non-controlling interest in consolidated subsidiary			(657)	(735)
Employee stock purchases			27	20
Intercompany transfers			(1,398)	21,940
Net cash provided by (used in) financing activities			(2,028)	21,225
Net increase (decrease) in cash and cash equivalents			3,479	(385)
Cash and cash equivalents, beginning of period			5,304	3,577	3,577
Cash and cash equivalents, end of period	8,783	3,192	8,783	3,192	5,304
Parent
Cash flows from operating activities:
Net income	4,541	2,101	11,208	14,526
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization			1,386	310
Interest expense related to amortization of debt issue costs and debt discount			1,606	1,184
Debt pre-payment premiums				93
Stock-based compensation			574	984
Deferred income taxes			3,537	1,675
Tax benefit from exercise of stock appreciation rights and vesting of restricted stock			(5,860)	(2)
Equity in earnings of subsidiaries	(15,928)	(11,021)	(33,493)	(29,647)
Decrease in accounts payable and accrued liabilities			(1,462)	(15,514)
Other changes in operating assets and liabilities, net			10,622	3,428
Net cash provided by (used in) operating activities			(11,882)	(22,963)
Cash flows from investing activities:
Purchase of property, plant and equipment			(1,499)	(1,758)
Net decrease (increase) in long-term receivables and deposits			3,167	(161)
Net change in other assets			507	(2,265)
Net cash provided by (used in) investing activities			2,175	(4,184)
Cash flows from financing activities:
Payments on long-term debt			(15,000)	(5,874)
Debt pre-payment premiums				(93)
Employee stock purchases			74	129
Tax benefit from exercise of stock appreciation rights and vesting of restricted stock			5,860	2
Intercompany transfers			5,792	(40,908)
Net cash provided by (used in) financing activities			(3,274)	(46,744)
Net increase (decrease) in cash and cash equivalents			(12,981)	(73,891)
Cash and cash equivalents, beginning of period			32,982	113,201	113,201
Cash and cash equivalents, end of period	$ 20,001	$ 39,310	$ 20,001	$ 39,310	$ 32,982