GUARANTOR AND NON-GUARANTOR FINANCIAL INFORMATION - Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
CONSOLIDATED CONDENSED STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Net income (loss)	$ (22,532)	$ (21,799)	$ (48,818)	$ (35,063)	$ (72,835)	$ (21,200)	$ 21,205	$ 16,002	$ (128,212)	$ (56,828)	$ 420,427
Other comprehensive income (loss), net of income taxes:
Unrealized (appreciation) depreciation on securities, net											(80,217)
Unrealized (appreciation) depreciation on securities, net									(829)	2,772	(80,217)
Reclassification of realized (gains) losses in net income, net										926
Minimum pension liability adjustments, net									3,333	(2,525)	(4,286)
Other comprehensive income (loss)									2,504	1,173	(84,503)
Comprehensive income (loss)									(125,708)	(55,655)	335,924
Reportable Legal Entities | Guarantor/Parent
CONSOLIDATED CONDENSED STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Net income (loss)									(128,212)	(56,828)	420,427
Other comprehensive income (loss), net of income taxes:
Minimum pension liability adjustments, net									860	(63)	(666)
Other comprehensive income (loss)									860	(63)	(666)
Comprehensive income (loss)									(127,352)	(56,891)	419,761
Reportable Legal Entities | Issuer Subsidiary
CONSOLIDATED CONDENSED STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Net income (loss)									(113,892)	(46,856)	425,302
Other comprehensive income (loss), net of income taxes:
Unrealized (appreciation) depreciation on securities, net											(80,217)
Unrealized (appreciation) depreciation on securities, net									(829)	2,772
Reclassification of realized (gains) losses in net income, net										926
Minimum pension liability adjustments, net									2,473	(2,462)	(3,620)
Other comprehensive income (loss)									1,644	1,236	(83,837)
Comprehensive income (loss)									(112,248)	(45,620)	341,465
Reportable Legal Entities | Non-Guarantor Subsidiaries
CONSOLIDATED CONDENSED STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Net income (loss)									(10,332)	(14,782)	(11,088)
Other comprehensive income (loss), net of income taxes:
Comprehensive income (loss)									(10,332)	(14,782)	(11,088)
Eliminations
CONSOLIDATED CONDENSED STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Net income (loss)									124,224	61,638	(414,214)
Other comprehensive income (loss), net of income taxes:
Comprehensive income (loss)									$ 124,224	$ 61,638	$ (414,214)