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Equity Incentive Plan [Line Items]

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Share Based Compensation Arrangement By Employee Stock Purchase Program Number Of Shares Available For Purchase

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Share Based Compensation Arrangement By Share Based Payment Award Employee Stock Purchase Plan Offering Term

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Share Based Compensation Arrangement By Share Based Payment Award Options Vesting Percentage Year One

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Share Based Compensation Arrangement By Share Based Payment Award Options Vesting Percentage Year Two

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Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Shares Eligible for Subsequent Vesting

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Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Percentage of Shares Eligible for Subsequent Vesting

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Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Measurement Period

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Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Performance-Based Units Awarded

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Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Performance-Based Units Awarded based on performance at target

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Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Performance-Based Units Awarded, Maximum

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Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Potentially Vested Shares, Percentage

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Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Quarterly Dividends in Period

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- Definition

Unrecognized cost of unvested share-based compensation awards.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The cash outflow to reacquire common stock during the period.

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Amount of cash outflow to satisfy an employee's income tax withholding obligation as part of a net-share settlement of a share-based award.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The net total number of shares (or other type of equity) under an equity-based award plan, other than a stock option plan, that were granted, vested and forfeited during the reporting period.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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- Definition

Number of additional shares authorized for issuance under an established share-based compensation plan.

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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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The number of shares purchased on the open market during the period for issuance to employees under the plan.

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Description of pertinent provisions of equity-based compensation awards that have actual or potential impact upon the company's financial statements.

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Purchase price of common stock expressed as a percentage of its fair value.

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Number of shares issued during the period as a result of an employee stock purchase plan.

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-Publisher FASB
-Name Accounting Standards Codification
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-Name Regulation S-X (SX)
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-Paragraph 29, 30
-Article 5

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Equity Incentive Plans - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended	12 Months Ended
	Feb. 08, 2012	Feb. 29, 1996	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014	Feb. 22, 1996
Equity Incentive Plan [Line Items]
Awards granted			1,690,582	1,513,281	1,517,057
Shares available for grant			4,363,536
Shares of common stock available for purchase			212,928
Additional shares of common stock available for purchase	1,000,000
Maximum percentage of base pay withheld and applied toward the purchase of shares	10.00%
Stock purchase under employee stock purchase plan			3,787,072
Board of Director Units
Equity Incentive Plan [Line Items]
Awards granted			86,082	69,281	82,095
Stock Compensation Plan
Equity Incentive Plan [Line Items]
Vesting period			4 years
Share-based Compensation Arrangement by Share-based Payment Award, Terms of Award			P10Y
Restricted stock
Equity Incentive Plan [Line Items]
Vesting period			3 years
Awards granted			1,690,582
Awards granted (USD per share)			$ 10.84	$ 11.89	$ 9.49
Fair value of restricted stock awards vested			$ 14.3	$ 8.4	$ 5.6
Unrecognized compensation cost			$ 15.1
Unrecognized compensation cost, estimated weighted average amortization period			1 year 8 months 1 day
Payments Related to Tax Withholding for Share-based Compensation			$ 4.4	$ 2.3	$ 1.4
Awards forfeited (in shares)			(1,189,057)
Employee Stock Purchase Plan Nineteen Ninety Five Plan [Member]
Equity Incentive Plan [Line Items]
Share Based Compensation Arrangement By Share Based Payment Award Employee Stock Purchase Plan Offering Term		6 months
Performance Based
Equity Incentive Plan [Line Items]
Maximum award over targeted number of awards			100.00%
Shares that could vest under terms of award					1,297,546
Shares that could vest under terms of award, percent					154.70%
Number of shares over the target grant				351,066
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Potentially Vested Shares, Percentage			40.00%	40.00%
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Measurement Period			3 years
Performance Based \| Maximum
Equity Incentive Plan [Line Items]
Maximum award over targeted number of awards			200.00%
Performance Based \| Minimum
Equity Incentive Plan [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Percentage of Performance-Based Units Awarded			0.00%
Performance Based \| Share-based Compensation Award, Tranche Two [Member]
Equity Incentive Plan [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Measurement Period			3 years
Time Based
Equity Incentive Plan [Line Items]
Awards granted			744,250	597,250	596,212
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Period Increase (Decrease)					458,796
Restricted Stock Units (RSUs) [Member]
Equity Incentive Plan [Line Items]
Vesting period			3 years
Performance Shares [Member]
Equity Incentive Plan [Line Items]
Awards granted				846,750	838,750
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Period Increase (Decrease)				495,684
Equity Incentive Plan 2000
Equity Incentive Plan [Line Items]
Shares of common stock reserved for issuance			9,000,000
Equity Incentive Plan 2000 \| Restricted stock
Equity Incentive Plan [Line Items]
Vesting period			3 years
Share Based Compensation Arrangement By Share Based Payment Award Options Vesting Percentage Year One			33.33%
Share Based Compensation Arrangement By Share Based Payment Award Options Vesting Percentage Year Two			33.33%
Share Based Compensation Arrangement By Share Based Payment Award Options Vesting Percentage Year Three			33.34%
Equity Incentive Plan 2000 \| Restricted stock \| Share Vesting Over Three Year Period [Member]
Equity Incentive Plan [Line Items]
Share Based Compensation Arrangement By Share Based Payment Award Options Vesting Percentage Year One
Share Based Compensation Arrangement By Share Based Payment Award Options Vesting Percentage Year Two			50.00%
Share Based Compensation Arrangement By Share Based Payment Award Options Vesting Percentage Year Three			50.00%
Equity Incentive Plan Two Thousand Fifteen
Equity Incentive Plan [Line Items]
Shares of common stock reserved for issuance			5,000,000
Equity Incentive Plan Two Thousand Fifteen \| Performance Based
Equity Incentive Plan [Line Items]
Awards granted			860,250
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Potentially Vested Shares, Percentage			60.00%
Percentage of award for performance at target			100.00%
Equity Incentive Plan Two Thousand Fifteen \| Performance Based \| Maximum
Equity Incentive Plan [Line Items]
Maximum award over targeted number of awards			200.00%
Equity Incentive Plan Two Thousand Fifteen \| Performance Based \| Minimum
Equity Incentive Plan [Line Items]
Percentage of the award for performance below the minimum threshold			0.00%
ESPP Plan Amendment
Equity Incentive Plan [Line Items]
Shares of common stock reserved for issuance	4,000,000					3,000,000
Employee Stock Purchase Plan
Equity Incentive Plan [Line Items]
Employee stock purchase plan, price per share percentage			85.00%
Employee Stock Purchase Plan Nineteen Ninety Five Plan [Member]
Equity Incentive Plan [Line Items]
Shares issued (in shares)			235,727	200,700
Payments for repurchase of common stock			$ 1.9	$ 1.8
Granville-Phillips [Member] \| Time Based
Equity Incentive Plan [Line Items]
Awards granted			8,500
Director [Member] \| Restricted Stock Units (RSUs) [Member]
Equity Incentive Plan [Line Items]
Awards granted			55,380	49,267	57,603
Restricted Stock Units (RSUs) [Member] \| Director [Member]
Equity Incentive Plan [Line Items]
Awards granted			25,560	13,318	24,492
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Quarterly Dividends in Period			5,142	6,876