CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Net income		$ 55,209	$ 75,687	$ 67,267	$ 91,241
Other comprehensive income:
Unrealized gain on pension plan obligation	[1]	648	558	1,296	1,114
Tax effect of unrealized gain on pension plan		(268)	(229)	(535)	(459)
Total other comprehensive income		380	329	761	655
Total comprehensive income		$ 55,589	$ 76,016	$ 68,028	$ 91,896

[1] This item is included in the computation of net periodic pension cost.