Long-Term Debt - Revolving Credit Facility (Details) - Revolving Credit Facility	3 Months Ended
	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 02, 2016 USD ($)
Line of Credit Facility [Line Items]
Maximum borrowing capacity			$ 506,000,000
Borrowings outstanding	$ 0	$ 0
Letters of credit outstanding	0	$ 0
Revolving Credit Facility with Conversion Election Agreement
Line of Credit Facility [Line Items]
Maximum borrowing capacity			466,000,000
Revolving Credit Facility - Amended - Matures In April 2017
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 8,000,000		32,000,000
Revolving Credit Facility - Amended - Matures In February 2019
Line of Credit Facility [Line Items]
Maximum borrowing capacity			$ 498,000,000
Amended Revolving Credit Facility
Line of Credit Facility [Line Items]
Collateral test, maximum ratio	1.0
Value of company assets collateralized	$ 677,000,000
Maximum limit on issuance, letters of credit	$ 100,000,000
Triggering Event One
Line of Credit Facility [Line Items]
Debt-to-EBITDA ratio	2.25
LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate	3.25%
Unused capacity, commitment fee percentage	0.50%
Prime Rate | Overnight Revolving Credit Loans
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.25%