Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Consolidated Statements of Comprehensive Income
Net income	$ (21,214)	$ 90,860	$ 149,537	$ 203,042	$ 168,688	$ 192,279	$ 174,570	$ 173,182	$ 422,225	$ 708,719	$ 736,639
Other comprehensive income, net of income taxes:
Unrealized appreciation (depreciation) on securities, net of income taxes of ($50.6) million at September 30, 2015, ($15.5) million at September 30, 2014 and $34.2 million at September 30, 2013									(80,217)	(19,006)	46,853
Reclassification of realized gains in net income, net of income taxes of ($17.5) million at September 30, 2014 and ($60.8) million at September 30, 2013										(27,737)	(92,543)
Minimum pension liability adjustments, net of income taxes of ($2.5) million at September 30, 2015, ($1.5) million at September 30, 2014 and $6.6 million at September 30, 2013									(4,286)	(2,661)	11,413
Other comprehensive loss									(84,503)	(49,404)	(34,277)
Comprehensive income									$ 337,722	$ 659,315	$ 702,362