Fair Value Measurements - Schedule of Available-for-sale Securities Reconciliation Table (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Sep. 30, 2017
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 87,241	$ 77,244
Gross Unrealized Gain	10,910	11,203
Gross Unrealized Loss	(727)	(38)
Fair Value	97,424	88,409
Domestic equity mutual funds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	28,283	25,361
Gross Unrealized Gain	8,973	8,920
Gross Unrealized Loss	(293)	0
Fair Value	36,963	34,281
Foreign equity mutual funds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	4,656	4,581
Gross Unrealized Gain	1,929	2,235
Gross Unrealized Loss	0	0
Fair Value	6,585	6,816
Bond mutual funds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	21,673	16,391
Gross Unrealized Gain	0	2
Gross Unrealized Loss	(295)	(22)
Fair Value	21,378	16,371
Bonds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	30,434	29,074
Gross Unrealized Gain	8	46
Gross Unrealized Loss	(139)	(16)
Fair Value	30,303	29,104
Money market funds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	2,195	1,837
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Fair Value	$ 2,195	$ 1,837

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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