CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income		$ 114,702	$ 73,353	$ 149,631	$ 123,635
Other comprehensive income, net of tax
Unrealized gain on available for sale securities, net of tax of $(670), $(3,154), $(4,456), and $(5,768), respectively		1,408	4,500	6,923	8,201
Net unrealized gain on derivatives, net of tax of $0, $(21), $0 and $(2), respectively	[1]	0	38	0	5
Adjustment to postemployment benefit obligation, net of tax of $(217), $(175), $(434), and $(349) respectively		318	257	635	513
Other comprehensive income		1,726	4,795	7,558	8,719
Comprehensive income		$ 116,428	$ 78,148	$ 157,189	$ 132,354

[1] Effective January 1, 2016, the Company elected not to designate its foreign currency derivatives as accounting hedges and, as a result, changes in fair value of the effective portion of the hedges are no longer recorded in OCI. See Note 4 Derivative Instruments for more information on these transactions.