Business Combinations (Details Textual) (USD $)							3 Months Ended	6 Months Ended
	Dec. 31, 2012	Mar. 31, 2012 Branch	Dec. 31, 2011	Mar. 31, 2011	Mar. 31, 2011 Midwest Bank and Trust Company [Member]	May 14, 2010 Midwest Bank and Trust Company [Member]	Mar. 31, 2012 George Washington Savings Bank [Member]	Jun. 30, 2011 George Washington Savings Bank [Member]
Business Acquisition [Line Items]
Number of branches		24
Cash received to assume net liabilities							$ 40,200,000
Bargain purchase gain								1,000,000
Bargain purchase, net of tax								700,000
Cash payment made by bank to FDIC						227,500,000
Goodwill	$ 460,044,000	$ 460,044,000	$ 460,044,000	$ 460,044,000	$ 272,100,000