CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net income	$ 110,043	$ 86,952	$ 59,849
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	25,876	25,930	26,031
Provision for doubtful accounts	185	26	588
Share-based compensation expense	18,517	13,004	13,787
Transition tax for accumulated foreign earnings, Income tax expense	11,340	0	0
Deferred income tax expense (benefit)	10,835	392	(1,757)
Non-cash foreign exchange (gain)	(873)	435	(1,144)
Loss/(Gain) on disposal of property, plant and equipment	91	(1,820)	103
Impairment of assets	0	860	1,079
Realized loss on the sale of available-for-sale securities	96	0	0
(Gain) on sale of assets	(956)	0	0
Other	1,666	188	815
Changes in operating assets and liabilities:
Accounts receivable	(12,068)	(3,986)	(8,017)
Inventories	(442)	(1,220)	3,351
Prepaid expenses and other assets	(5,818)	(1,576)	3,935
Accounts payable	128	892	(478)
Accrued expenses, income taxes payable and other liabilities	10,245	21,292	(2,931)
Net cash provided by operating activities	168,865	141,369	95,211
Cash flows from investing activities:
Additions to property, plant and equipment	(21,308)	(21,174)	(17,670)
Proceeds from the sale of property, plant and equipment	0	1,216	17
Acquisition of business, net of cash acquired	0	0	(126,976)
Proceeds from the sale of assets	3,027	0	0
Purchases of available-for-sale securities	(209,048)	0	0
Proceeds from the sale and maturities of investment securities	214,460	175	200
Settlement of net investment hedge	(9,882)	0	0
Net cash used in investing activities	(22,751)	(19,783)	(144,429)
Cash flows from financing activities:
Repayment of long-term debt	(144,375)	(10,938)	(8,750)
Dividends paid	(30,730)	(19,041)	(8,658)
Repurchases of common stock	(44,288)	(14,208)	(28,818)
Proceeds from issuance of stock	23,031	30,615	19,512
Tax benefits associated with share-based compensation expense	0	6,557	2,305
Principal payments under capital lease obligations	(1,200)	0	0
Net cash used in financing activities	(197,562)	(7,015)	(24,409)
Effect of exchange rate changes on cash	6,479	(4,160)	6,916
Increase (decrease) in cash	(44,969)	110,411	(66,711)
Cash and cash equivalents at beginning of year	397,890	287,479	354,190
Cash and cash equivalents at end of year	352,921	397,890	287,479
Supplemental disclosure of cash flow information:
Cash paid for income taxes	20,345	13,321	7,246
Cash paid for interest	2,464	4,128	4,307
Supplemental disclosure of non-cash investing and financing activities:
Purchases of property, plant and equipment in accrued liabilities and accounts payable at the end of period	$ 1,975	$ 1,488	$ 1,005