Assets Held for Sale and Discontinued Operations - Operating Results of Discontinued Operations (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income tax provision (benefit)		$ (3,200)		$ (3,100)
Net (loss) income	$ (6,647)	1,774	$ (9,267)	6,525
Solar Segment | Discontinued Operations, Held-for-sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenues, net of returns and allowances	8,153	11,668	14,381	58,163
Cost of sales	9,229	8,525	15,352	44,643
Gross (loss) profit	(1,076)	3,143	(971)	13,520
Selling, general and administrative	4,082	3,159	5,677	7,315
Research, development and engineering	831	1,404	1,911	2,720
Restructuring charges	591	0	601	0
Operating (loss) income	(6,580)	(1,420)	(9,160)	3,485
Interest income (expense) and other income, net	(48)	(6)	(70)	(72)
(Loss) income from discontinued operations before income taxes	(6,628)	(1,426)	(9,230)	3,413
Income tax provision (benefit)	19	(3,200)	37	(3,112)
Net (loss) income	$ (6,647)	$ 1,774	$ (9,267)	$ 6,525