Basis of Presentation and Summary of Significant Accounting Policies - Accounting Standards Update (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Sep. 30, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other assets	$ 7,522	$ 7,086
Assets	2,213,158	2,409,295
Total debt (net of premium and debt issuance costs)	1,331,878	1,516,367
Total liabilities	1,570,305	1,778,872
Total liabilities and stockholders’ equity	$ 2,213,158	2,409,295
Accounting Standards Update 2015-03
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total debt (net of premium and debt issuance costs)		1,516,367
Accounting Standards Update 2015-03 | As initially reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other assets		18,994
Assets		2,421,203
Total debt (net of premium and debt issuance costs)		1,528,275
Total liabilities		1,790,780
Total liabilities and stockholders’ equity		2,421,203
Accounting Standards Update 2015-03 | Change for adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other assets		(11,908)
Assets		(11,908)
Total debt (net of premium and debt issuance costs)		(11,908)
Total liabilities		(11,908)
Total liabilities and stockholders’ equity		$ (11,908)