Fair Values (Details) - USD ($) $ in Thousands		Mar. 31, 2018	Sep. 30, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Current portion of long term obligation, amortized cost		$ 7,400
Noncurrent portion of long term obligation, amortized cost		449,700
Fair Value, Measurements, Recurring | Prepaid and other assets: | Fair Value, Inputs, Level 1 | Mutual funds — Deferred comp and supplemental plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mutual funds - Deferred comp and supplemental plan	[1]	19,474	$ 17,585
Fair Value, Measurements, Recurring | Prepaid and other assets: | Fair Value, Inputs, Level 2 | Mutual funds — Deferred comp and supplemental plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mutual funds - Deferred comp and supplemental plan	[1]	0	0
Fair Value, Measurements, Recurring | Prepaid and other assets: | Estimate of Fair Value Measurement | Mutual funds — Deferred comp and supplemental plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mutual funds - Deferred comp and supplemental plan	[1]	19,474	17,585
Fair Value, Measurements, Recurring | Assets | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities, fair value disclosure		76,765	79,681
Fair Value, Measurements, Recurring | Assets | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities, fair value disclosure		42,167	70,757
Fair Value, Measurements, Recurring | Assets | Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities, fair value disclosure		118,932	150,438
Fair Value, Measurements, Recurring | Liabilities | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities, fair value disclosure		76,765	79,681
Fair Value, Measurements, Recurring | Liabilities | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities, fair value disclosure		40,673	69,282
Fair Value, Measurements, Recurring | Liabilities | Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets and liabilities, fair value disclosure		117,438	148,963
Fair Value, Measurements, Recurring | Money market fund deposits | Cash equivalents: | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure		57,047	61,811
Fair Value, Measurements, Recurring | Money market fund deposits | Cash equivalents: | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Fair Value, Measurements, Recurring | Money market fund deposits | Cash equivalents: | Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure		57,047	61,811
Fair Value, Measurements, Recurring | Money market fund deposits | Prepaid and other assets: | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value Disclosure	[1]	244	285
Fair Value, Measurements, Recurring | Money market fund deposits | Prepaid and other assets: | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value Disclosure	[1]	0	0
Fair Value, Measurements, Recurring | Money market fund deposits | Prepaid and other assets: | Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value Disclosure	[1]	244	285
Fair Value, Measurements, Recurring | U.S. Treasury and agency obligations | Cash equivalents: | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	[2]	0	0
Fair Value, Measurements, Recurring | U.S. Treasury and agency obligations | Cash equivalents: | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	[2]	0	14,986
Fair Value, Measurements, Recurring | U.S. Treasury and agency obligations | Cash equivalents: | Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	[2]	0	14,986
Fair Value, Measurements, Recurring | U.S. Treasury and agency obligations | Short-term investments: | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value Disclosure	[2]	0	0
Fair Value, Measurements, Recurring | U.S. Treasury and agency obligations | Short-term investments: | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value Disclosure	[2]	14,993	21,087
Fair Value, Measurements, Recurring | U.S. Treasury and agency obligations | Short-term investments: | Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value Disclosure	[2]	14,993	21,087
Fair Value, Measurements, Recurring | Corporate notes and obligations | Short-term investments: | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value Disclosure	[2]	0	0
Fair Value, Measurements, Recurring | Corporate notes and obligations | Short-term investments: | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value Disclosure	[2]	7,140	11,423
Fair Value, Measurements, Recurring | Corporate notes and obligations | Short-term investments: | Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value Disclosure	[2]	7,140	11,423
Fair Value, Measurements, Recurring | Commercial paper | Cash equivalents: | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	[3]	0	0
Fair Value, Measurements, Recurring | Commercial paper | Cash equivalents: | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	[3]	4,975	21,991
Fair Value, Measurements, Recurring | Commercial paper | Cash equivalents: | Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	[3]	4,975	21,991
Fair Value, Measurements, Recurring | Commercial paper | Short-term investments: | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value Disclosure	[2]	0	0
Fair Value, Measurements, Recurring | Commercial paper | Short-term investments: | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value Disclosure	[2]	14,994	0
Fair Value, Measurements, Recurring | Commercial paper | Short-term investments: | Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value Disclosure	[2]	14,994	0
Fair Value, Measurements, Recurring | Foreign currency contracts | Prepaid and other assets: | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency contracts	[3]	0	0
Fair Value, Measurements, Recurring | Foreign currency contracts | Prepaid and other assets: | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency contracts	[3]	65	1,270
Fair Value, Measurements, Recurring | Foreign currency contracts | Prepaid and other assets: | Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency contracts	[3]	65	1,270
Fair Value, Measurements, Recurring | Foreign currency contracts | Other current liabilities: | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency contracts	[1]	0	0
Fair Value, Measurements, Recurring | Foreign currency contracts | Other current liabilities: | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency contracts	[1]	(1,494)	(1,475)
Fair Value, Measurements, Recurring | Foreign currency contracts | Other current liabilities: | Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency contracts	[1]	$ (1,494)	$ (1,475)

[1] The fair value of mutual funds is determined based on quoted market prices. Securities traded on a national exchange are stated at the last reported sales price on the day of valuation; other securities traded in over-the-counter markets and listed securities for which no sale was reported on that date are stated as the last quoted bid price.

[2] Valuations are based upon quoted market prices in active markets involving similar assets. The market inputs used to value these instruments generally consist of market yields, reported trades, broker/dealer quotes or alternative pricing sources with reasonable levels of price transparency. Pricing sources include industry standard data providers, security master files from large financial institutions, and other third party sources which are input into a distribution-curve-based algorithm to determine a daily market value. This creates a “consensus price” or a weighted average price for each security.

[3] The principal market in which we execute our foreign currency contracts is the institutional market in an over-the-counter environment with a relatively high level of price transparency. The market participants usually are large commercial banks. Our foreign currency contracts’ valuation inputs are based on quoted prices and quoted pricing intervals from public data sources and do not involve management judgment. See Note 6, "Derivative Instruments and Hedging Activities".