Long-Term Debt - Summary of Long-Term Debt (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014		Sep. 30, 2013
Debt Instrument
Long-term debt	$ 1,512,685		$ 1,263,232
Senior Notes | 6.5% Senior Notes
Debt Instrument
Long-term debt	657,685		658,232
Stated interest rate	6.50%		6.50%
Revolving Credit Facility | 2011 Revolving Credit Facility
Debt Instrument
Long-term debt	$ 855,000		$ 605,000
Market adjustable interest rate (per annum)	2.90%	[1]	3.00%	[1]

[1] After the impact of our interest rate swaps.