Guarantor and Non-Guarantor Financial Information - Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
CONDENSED CONSOLIDATING STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Net (loss) income	$ (8,008)	$ (21,799)	$ 480,219	$ (105,680)
Other comprehensive income (loss), net of income taxes:
Unrealized appreciation (depreciation) on securities, net	13,826	(6,899)	5,657	(4,994)
Minimum pension liability adjustments, net	337	365	985	1,097
Other comprehensive income (loss)	14,163	(6,534)	6,642	(3,897)
Comprehensive income (loss)	6,155	(28,333)	486,861	(109,577)
Reportable Legal Entities \| Guarantor/Parent
CONDENSED CONSOLIDATING STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Net (loss) income	(8,008)	(21,799)	480,219	(105,680)
Other comprehensive income (loss), net of income taxes:
Minimum pension liability adjustments, net	101	104	295	316
Other comprehensive income (loss)	101	104	295	316
Comprehensive income (loss)	(7,907)	(21,695)	480,514	(105,364)
Reportable Legal Entities \| Issuer Subsidiary
CONDENSED CONSOLIDATING STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Net (loss) income	(6,482)	(19,960)	494,775	(98,209)
Other comprehensive income (loss), net of income taxes:
Unrealized appreciation (depreciation) on securities, net	13,826	(6,899)	5,657	(4,994)
Minimum pension liability adjustments, net	236	261	690	781
Other comprehensive income (loss)	14,062	(6,638)	6,347	(4,213)
Comprehensive income (loss)	7,580	(26,598)	501,122	(102,422)
Reportable Legal Entities \| Non-Guarantor Subsidiaries
CONDENSED CONSOLIDATING STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Net (loss) income	(494)	365	2,990	(11,844)
Other comprehensive income (loss), net of income taxes:
Comprehensive income (loss)	(494)	365	2,990	(11,844)
Eliminations
CONDENSED CONSOLIDATING STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Net (loss) income	6,976	19,595	(497,765)	110,053
Other comprehensive income (loss), net of income taxes:
Comprehensive income (loss)	$ 6,976	$ 19,595	$ (497,765)	$ 110,053

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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