Capital Stock (Detail Textuals) (USD $)	1 Months Ended	2 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended		1 Months Ended		0 Months Ended	1 Months Ended	2 Months Ended	3 Months Ended		6 Months Ended		1 Months Ended		2 Months Ended	6 Months Ended
	Apr. 30, 2013	Dec. 13, 2012	Jul. 31, 2013	Jul. 31, 2012	Jul. 31, 2013	Jul. 31, 2012	Jan. 31, 2013	Jul. 12, 2013	Apr. 30, 2013 2014 Senior Notes [Member]	Jul. 12, 2013 2014 Senior Notes [Member]	Mar. 15, 2013 Series A Preferred Stock [Member]	Mar. 14, 2013 Series A Preferred Stock [Member]	Dec. 13, 2012 Series A Preferred Stock [Member]	Jul. 31, 2013 Series A Preferred Stock [Member]	Jul. 31, 2012 Series A Preferred Stock [Member]	Jul. 31, 2013 Series A Preferred Stock [Member]	Jul. 31, 2012 Series A Preferred Stock [Member]	Apr. 30, 2013 Class A common stock [Member]	Mar. 14, 2013 Class A common stock [Member]	Dec. 13, 2012 Class A common stock [Member]	Jul. 31, 2013 Class A common stock [Member]	Jul. 12, 2013 Class A common stock [Member]	Mar. 13, 2013 Class A common stock [Member]
Class of Stock [Line Items]
Exchange of preferred stock, aggregate liquidation preference amount													$ 209,447,600
Exchange of preferred stock, preferred shares exchanged													4,188,952
Exchange of preferred stock, common shares issued for preferred stock																				13,852,435
Exchange of preferred stock, initial conversion price																				$ 15.12
Cash payments related to conversion of preferred stock for Class A common stock		19,069,000
Conversion of stock, shares converted												109,768							362,990
Stock redeemed during period, Shares											101,270					(101,000)
Stock redeemed during period, Value					(5,063,000)						5,100,000					(5,063,000)
Shares received upon settlement of equity call hedge																							765,134
Value per share of Class A common stock received upon settlement of equity call hedge																							$ 16.82
Class A common stock received upon settlement of equity call hedge																							12,868,000
Proceeds from equity call hedge related to Series A preferred stock issuance					10,231,000	0
Preferred Stock (Textual) [Abstract]
Preferred dividends			0	3,850,000	185,000	7,700,000	13,060,000							0	3,850,000	185,000	7,700,000
Aggregate principal amount of Senior Notes exchanged for Class A common stock									138,853,000
Issuance of Class A shares in exchange for Senior Notes due 2014																		9,549,721			13,679,000
Cash payment for additional exchange consideration, accrued interest and in lieu of fractional shares	4,860,000
Aggregate principal amount of Senior Notes put to the Company										60,033,000
Number of shares received by the note holder upon a put																						4,128,806
Cash payments for interest payable and in lieu of fractional shares for put transaction								$ 1,088,000