Guarantor and Non-Guarantor financial information - Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
CONSOLIDATED CONDENSED STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Net income (loss)	$ (35,063)	$ 16,002
Other comprehensive income (loss), net of income taxes:
Unrealized (appreciation) depreciation on securities, net	12,412	(11,010)
Minimum pension liability adjustments, net	366	313
Other comprehensive income (loss)	12,778	(10,697)
Comprehensive income (loss)	(22,285)	5,305
Reportable Legal Entities | Guarantor/Parent
CONSOLIDATED CONDENSED STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Net income (loss)	(35,063)	16,002
Other comprehensive income (loss), net of income taxes:
Minimum pension liability adjustments, net	106	107
Other comprehensive income (loss)	106	107
Comprehensive income (loss)	(34,957)	16,109
Reportable Legal Entities | Issuer Subsidiary
CONSOLIDATED CONDENSED STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Net income (loss)	(32,865)	17,300
Other comprehensive income (loss), net of income taxes:
Unrealized (appreciation) depreciation on securities, net	12,412	(11,010)
Minimum pension liability adjustments, net	260	206
Other comprehensive income (loss)	12,672	(10,804)
Comprehensive income (loss)	(20,193)	6,496
Reportable Legal Entities | Non-Guarantor Subsidiaries
CONSOLIDATED CONDENSED STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Net income (loss)	202	(7,948)
Other comprehensive income (loss), net of income taxes:
Comprehensive income (loss)	202	(7,948)
Eliminations
CONSOLIDATED CONDENSED STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Net income (loss)	32,663	(9,352)
Other comprehensive income (loss), net of income taxes:
Comprehensive income (loss)	$ 32,663	$ (9,352)