Earnings Per Share - Schedule of Calculation of Basic and Diluted Earnings Per Share of Common Stock Outstanding (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended												12 Months Ended
	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2011
Earnings Per Share Basic And Diluted [Line Items]
Net income													$ 142,407	$ 329,541	$ 135,916
Weighted average shares outstanding													68,990	71,297	70,992
Total weighted average shares outstanding													69,736	72,083	71,635
Earnings per share	$ 0.08	$ 0.50	$ 0.69	$ 0.79	$ 0.69	$ 2.41	$ 0.83	$ 0.68	$ 0.27	$ 0.51	$ 0.75	$ 0.39	$ 2.06	$ 4.62	$ 1.91
Basic [Member]
Earnings Per Share Basic And Diluted [Line Items]
Net income													142,407	329,541	135,916
Weighted average shares outstanding													68,990	71,297	70,992
Employee stock options	0				0				0				0	0	0
Total weighted average shares outstanding													68,990	71,297	70,992
Earnings per share													$ 2.06	$ 4.62	$ 1.91
Diluted [Member]
Earnings Per Share Basic And Diluted [Line Items]
Net income													$ 142,407	$ 329,541	$ 135,916
Weighted average shares outstanding													68,990	71,297	70,992
Employee stock options	746				786				643				746	786	643
Total weighted average shares outstanding													69,736	72,083	71,635
Earnings per share													$ 2.04	$ 4.57	$ 1.90