Cash Dividends (Details) (USD $)	1 Months Ended	12 Months Ended
	Dec. 31, 2012	Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2011
Cash Dividends (Textual) [Abstract]
Total cash dividends per share (dollars per share)		$ 4.98	$ 0.89	$ 1.49
Special cash dividend per share (dollars per share)	$ 4.00	$ 4.00		$ 0.67