Current and Deferred Income Tax Expense (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013
Deferred Income Tax Assets And Liabilities
Income before income taxes	$ 89,289	$ 70,796	$ 122,132	$ 85,465
Current tax expense	32,215	21,330	42,438	25,383
Deferred tax expense	4,858	7,787	8,190	8,651
Total tax expense	$ 37,073	$ 29,117	$ 50,628	$ 34,034