Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Consolidated Statements of Comprehensive Income (Loss)
Net income (loss)	$ 2,453	$ (8,008)	$ (11,879)	$ 500,106	$ (22,532)	$ (21,799)	$ (48,818)	$ (35,063)	$ 482,672	$ (128,212)	$ (56,828)
Other comprehensive income (loss), net of income taxes:
Unrealized appreciation (depreciation) on securities, net of income taxes of $3.3 million at September 30, 2018, ($0.5) million at September 30, 2017 and $1.7 million at September 30, 2016									9,001	(829)	2,772
Reclassification of realized losses in net income, net of income taxes of $0.6 million at September 30, 2016											926
Minimum pension liability adjustments, net of income taxes of $1.9 million at September 30, 2018, $1.9 million at September 30, 2017 and ($1.4) million at September 30, 2016									5,249	3,333	(2,525)
Other comprehensive income									14,250	2,504	1,173
Comprehensive income (loss)									$ 496,922	$ (125,708)	$ (55,655)