Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	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, 2012	Jun. 30, 2011	Jun. 30, 2010
Net Income	$ 43,327	$ 36,657	$ 38,525	$ 36,475	$ 36,574	$ 33,081	$ 36,045	$ 31,771	$ 154,984	$ 137,471	$ 117,870
Common share information:
Weighted average shares outstanding for basic earnings per share	86,595	86,824	86,572	86,403	86,335	86,218	85,770	85,469	86,599	85,948	84,558
Dilutive effect of stock options and restricted stock									688	739	823
Weighted average shares outstanding for diluted earnings per share	87,051	87,592	87,371	87,134	87,090	86,972	86,523	86,147	87,287	86,687	85,381
Basic earnings per share	$ 0.50	$ 0.42	$ 0.45	$ 0.42	$ 0.42	$ 0.38	$ 0.42	$ 0.37	$ 1.79	$ 1.60	$ 1.39
Diluted earnings per share	$ 0.50	$ 0.42	$ 0.44	$ 0.42	$ 0.42	$ 0.38	$ 0.42	$ 0.37	$ 1.78	$ 1.59	$ 1.38
Antidilutive stock options and restricted stock excluded from computation of earnings per share									0	12	602