CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Cash flows from operating activities
Net income (loss)	$ 62,612	$ (69,476)	$ 14,221
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	28,149	28,046	25,160
Gain on settlement of equity method investment	(1,847)
Impairment of other assets		807
Stock-based compensation	17,278	11,737	12,159
Amortization of premium on marketable securities and deferred financing costs	252	339	1,193
(Earnings) losses of equity method investments	(9,381)	(2,380)	164
Deferred income tax provision (benefit)	517	70,273	(2,173)
Loss on write-downs of assets held for sale			1,944
Pension settlement	(259)		232
Other gains on disposals of assets	(406)	(41)	(85)
Changes in operating assets and liabilities, net of acquisitions:
Accounts receivable	(11,178)	(1,796)	(5,134)
Inventories	(12,792)	8,565	(5,919)
Prepaid expenses and other current assets	(5,829)	(428)	(2,875)
Accounts payable	7,846	(5,143)	8,358
Deferred revenue	8,049	(3,290)	(6,779)
Accrued warranty and retrofit costs	1,602	290	(407)
Accrued compensation and tax withholdings	5,565	(3,234)	(1,148)
Accrued restructuring costs	(4,241)	3,860	(1,247)
Accrued pension costs	(32)	(811)	812
Accrued expenses and other current liabilities	10,319	2,229	5,251
Net cash provided by operating activities	96,224	39,547	43,727
Cash flows from investing activities
Purchases of property, plant and equipment	(12,677)	(12,848)	(16,146)
Purchases of technology intangibles	(240)
Purchases of marketable securities		(12,901)	(87,333)
Sales and maturities of marketable securities	3,590	139,388	104,008
Disbursement for a loan receivable		(1,821)
Acquisitions, net of cash acquired	(44,791)	(125,248)	(14,450)
Proceeds from liquidation of a joint venture			1,778
Purchases of other investments	(170)	(250)	(5,500)
Proceeds from sales of property, plant and equipment	100	2,806	6
Net cash used in investing activities	(54,188)	(10,874)	(17,637)
Cash flows from financing activities
Proceeds from line of credit		366
Proceeds from issuance of common stock	2,040	1,888	1,807
Payment of deferred financing costs	(28)	(708)
Repayment of debt assumed in business acquisition			(8,829)
Common stock dividends paid	(27,932)	(27,503)	(26,992)
Net cash used in financing activities	(25,920)	(25,957)	(34,014)
Effects of exchange rate changes on cash and cash equivalents	420	1,648	(5,468)
Net increase (decrease) in cash and cash equivalents	16,536	4,364	(13,392)
Cash and cash equivalents, beginning of period	85,086	80,722	94,114
Cash and cash equivalents, end of period	101,622	85,086	80,722
Supplemental disclosures:
Cash paid for interest	200	114	395
Cash paid for income taxes, net	8,142	$ 4,930	3,883
Supplemental disclosure of non-cash investing and financing activities:
Derecognition of a capital lease obligation and the related assets			$ 7,804
Deferred financing costs included in accrued expenses	423
Fair value of non-cash consideration for the acquisition of Cool Lab, LLC	$ 10,348