Employee Benefit Plans - Additional Information (Detail) (USD $)	12 Months Ended					12 Months Ended					12 Months Ended																12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2014 Significant Other Observable Inputs Level 2	Sep. 30, 2014 Significant Unobservable Inputs Level 3	Sep. 30, 2014 Minimum	Sep. 30, 2014 Frozen Defined Benefit Pension Plans Program	Sep. 30, 2013 Frozen Defined Benefit Pension Plans	Sep. 30, 2012 Frozen Defined Benefit Pension Plans	Sep. 30, 2011 Frozen Defined Benefit Pension Plans	Sep. 30, 2014 Other Postretirement Benefit Plan, Defined Benefit	Sep. 30, 2013 Other Postretirement Benefit Plan, Defined Benefit	Sep. 30, 2012 Other Postretirement Benefit Plan, Defined Benefit	Sep. 30, 2014 Domestic Fixed Income	Sep. 30, 2014 International Equities	Sep. 30, 2014 Domestic Equities	Sep. 30, 2014 Management	Sep. 30, 2014 Management And General Partner	Sep. 30, 2013 Management And General Partner	Sep. 30, 2012 Management And General Partner	Sep. 30, 2014 Management Incentive Compensation Plan	Sep. 30, 2013 Management Incentive Compensation Plan	Sep. 30, 2012 Management Incentive Compensation Plan	Sep. 30, 2014 Management Incentive Compensation Plan Executive Officer	Sep. 30, 2013 Management Incentive Compensation Plan Executive Officer	Sep. 30, 2012 Management Incentive Compensation Plan Executive Officer	Sep. 30, 2014 Employee and Consultant	Sep. 30, 2014 Termination of employment or consultation	Sep. 30, 2014 Chief executive officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Participant Contribution						0.00%
Maximum participant contribution	60.00%
Partnership aggregate contributions to defined contribution plans	$ 5,200,000	$ 4,900,000	$ 4,500,000								$ 500,000	$ 500,000	$ 500,000
Incentive distribution percentage of available cash in excess of minimum quarterly distribution																	50.00%
Minimum quarterly distribution																	0.0675
Gains interest cash proceeds percentage from the sale of general partner units																	50.00%
Participant's vested percentage of plan benefits																											100.00%	20.00%	33.333%
Partnership incentive distribution																		447,000	330,000	277,000	223,000	165,000	138,000	100,000	119,000	99,000
Maximum funded for red zone	65.00%
Maximum funded for yellow zone	80.00%
Minimum funded for green zone	80.00%
Partnership contributions in excess of 5% of the plan's total contributions in percentage	5.00%	5.00%	5.00%
Number of frozen defined benefit pension plans							2
Defined benefit plan funded status included in other long-term liabilities	5,100,000	4,300,000
Net actuarial loss balance in accumulated other comprehensive income to be amortized	26,600,000
Amount to be amortized from accumulated other comprehensive income	2,200,000
Rate pension plan assets expect to earn	5.50%
Discount rate to determine periodic pension expense	4.45%	3.50%	4.35%
Pension asset allocation														80.00%	5.00%	15.00%
Fair values of the Partnership's pension plan assets				0	0		65,379,000	60,028,000	60,303,000	52,434,000
Expected Pension Contribution Next Year	1,700,000
Expected benefit payments in years	5 years
Expected benefit payments over the next 5 years	4,400,000
Aggregate expected benefit payment for five years thereafter	$ 21,300,000