SHAREHOLDERS' EQUITY (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Pre-tax amounts:
Accumulated other comprehensive income (loss) before tax	$ (3,123)	$ 134,433	$ 218,004
Rollforward of accumulated other comprehensive income (loss), net of tax
Balance	4,890,977	4,443,727	3,834,998
Balance	4,897,452	4,890,977	4,443,727
Unrealized appreciation on securities
Pre-tax amounts:
Accumulated other comprehensive income (loss) before tax	27,021	157,838	237,214
Rollforward of accumulated other comprehensive income (loss), net of tax
Balance	97,418	144,161
Other comprehensive loss before reclassifications	(80,217)
Net current-period other comprehensive loss	(80,217)
Balance	17,201	97,418	144,161
Unrealized actuarial loss
Pre-tax amounts:
Accumulated other comprehensive income (loss) before tax	(30,144)	(23,405)	(19,210)
Rollforward of accumulated other comprehensive income (loss), net of tax
Balance	(14,292)	(11,631)
Amounts reclassified from accumulated other comprehensive loss	(4,286)
Net current-period other comprehensive loss	(4,286)
Balance	(18,578)	(14,292)	(11,631)
Accumulated Other Comprehensive Income.
Rollforward of accumulated other comprehensive income (loss), net of tax
Balance	83,126	132,530	166,807
Other comprehensive loss before reclassifications	(80,217)
Amounts reclassified from accumulated other comprehensive loss	(4,286)
Net current-period other comprehensive loss	(84,503)
Balance	$ (1,377)	$ 83,126	$ 132,530