Stockholders' Investment (Details) (USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended	1 Months Ended	3 Months Ended
	Apr. 30, 2012	Sep. 30, 2011 Common Class A [Member]	Apr. 30, 2012 Common Class A [Member]	Jan. 31, 2012 Common Class A [Member]	Oct. 31, 2011 Common Class A [Member]	Jul. 31, 2011 Common Class A [Member]
Stockholders' Equity (Textual) [Abstract]
Remained Shares to repurchase in connection with its repurchase plan			1,746,773			204,133
Number of shares reacquired		2,000,000			457,360
Value of reacquired shares in connection with its repurchase plan	$ 12,309				$ 12,309
Share repurchased			0	0