Senior and Subordinated Debt Senior and Subordinated Debt (Details Textuals) (USD $)	1 Months Ended	3 Months Ended		6 Months Ended			6 Months Ended	1 Months Ended									3 Months Ended		1 Months Ended	6 Months Ended
	Apr. 30, 2013	Jul. 31, 2013	Jul. 31, 2012	Jul. 31, 2013	Jul. 31, 2012	Jul. 12, 2013	Jul. 31, 2013 Puttable Equity-Linked Senior Notes due 2014 [Member]	Apr. 30, 2013 Puttable Equity-Linked Senior Notes due 2014 [Member]	Jul. 31, 2013 Puttable Equity-Linked Senior Notes due 2014 [Member]	Jul. 12, 2013 Puttable Equity-Linked Senior Notes due 2014 [Member]	Jan. 31, 2013 Puttable Equity-Linked Senior Notes due 2014 [Member]	Jul. 31, 2013 Senior Notes due 2015 [Member]	Mar. 29, 2013 Senior Notes due 2015 [Member]	Jan. 31, 2013 Senior Notes due 2015 [Member]	Jul. 31, 2013 Senior Notes due 2017 [Member]	Jan. 31, 2013 Senior Notes due 2017 [Member]	Jul. 31, 2013 Convertible Senior Notes due 2020 [Member] D	Jan. 31, 2013 Convertible Senior Notes due 2020 [Member]	Apr. 30, 2013 Class A common stock [Member]	Jul. 31, 2013 Class A common stock [Member]	Jul. 12, 2013 Class A common stock [Member]	Aug. 23, 2013 Subsequent Event [Member] Senior Notes due 2017 [Member]
Debt Instrument [Line Items]
Principal amount of notes redeemed													$ 53,253,000									$ 132,144,000
Interest rate									3.625%		3.625%	7.625%		7.625%	6.50%	6.50%	3.625%	3.625%
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
Loss on extinguishment of debt		(24,669,000)	0	(19,431,000)	719,000		4,762,000
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
Aggregate principal amount outstanding after put transaction										1,114,000
Senior notes issued																	300,000,000
Interest payable on notes																	semi-annually on February 15 and August 15
Net cash proceeds from issuance of Senior Notes																	291,250,000
Number of Class A common stock shares received by the note holder upon conversion																	41.3129
Principal amount of Senior Notes																	$ 1,000
Conversion price per share																	$ 24.21
Percentage of weighted average price of common stock equaled or exceeded conversion price																	130.00%
Weighted average price of common stock equaled or exceeded conversion price																	$ 31.47
Minimum trading days during which daily volume weighted average price exceeds or equals conversion price																	30
Number of consecutive trading days																	30 days
Minimum number of days after mailing redemption notice for effective redemption date																	30 days
Maximum number of days after mailing redemption notice for effective redemption date																	60 days