Corporate Debt (Narrative - Convertible Senior Subordinated Notes) (Details) (USD $)	12 Months Ended																												3 Months Ended						1 Months Ended		3 Months Ended	0 Months Ended	3 Months Ended				12 Months Ended				3 Months Ended						0 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2010	Mar. 31, 2011 October 2004 Notes [Member]	Mar. 31, 2011 February 2005 Notes [Member]	Mar. 31, 2012 Convertible Senior Subordinated Notes [Member]	Mar. 31, 2011 Convertible Senior Subordinated Notes [Member]	Mar. 31, 2010 Convertible Senior Subordinated Notes [Member]	Jul. 20, 2010 Convertible Senior Subordinated Notes [Member] New 2.9375% Notes [Member]	Jul. 20, 2010 Convertible Senior Subordinated Notes [Member] New 3.625% Notes [Member]	Mar. 31, 2012 Convertible Senior Subordinated Notes [Member] October 2004 Notes [Member]	Mar. 31, 2011 Convertible Senior Subordinated Notes [Member] October 2004 Notes [Member]	Mar. 31, 2010 Convertible Senior Subordinated Notes [Member] October 2004 Notes [Member]	Oct. 31, 2004 Convertible Senior Subordinated Notes [Member] October 2004 Notes [Member]	Mar. 31, 2012 Convertible Senior Subordinated Notes [Member] February 2005 Notes [Member]	Mar. 31, 2011 Convertible Senior Subordinated Notes [Member] February 2005 Notes [Member]	Mar. 31, 2010 Convertible Senior Subordinated Notes [Member] February 2005 Notes [Member]	Feb. 28, 2005 Convertible Senior Subordinated Notes [Member] February 2005 Notes [Member]	Mar. 31, 2012 Convertible Senior Subordinated Notes [Member] April 2009 Notes [Member]	Mar. 31, 2011 Convertible Senior Subordinated Notes [Member] April 2009 Notes [Member]	Mar. 31, 2010 Convertible Senior Subordinated Notes [Member] April 2009 Notes [Member]	Apr. 30, 2009 Convertible Senior Subordinated Notes [Member] April 2009 Notes [Member]	Mar. 31, 2012 Convertible Senior Subordinated Notes [Member] January 2012 Notes [Member]	Jan. 11, 2012 Convertible Senior Subordinated Notes [Member] January 2012 Notes [Member]	Mar. 31, 2011 Convertible Senior Subordinated Notes [Member] January 2012 Notes [Member]	Mar. 31, 2010 Convertible Senior Subordinated Notes [Member] January 2012 Notes [Member]	Mar. 31, 2012 On or Before March 15, 2012 [Member] Convertible Senior Subordinated Notes [Member] February 2005 Notes [Member]	Mar. 31, 2012 After March 15, 2012 [Member] Convertible Senior Subordinated Notes [Member] February 2005 Notes [Member]	Mar. 31, 2012 Issuer [Member] Convertible Senior Subordinated Notes [Member] October 2004 Notes [Member]	Mar. 31, 2012 Issuer [Member] Convertible Senior Subordinated Notes [Member] February 2005 Notes [Member]	Mar. 31, 2012 Issuer [Member] On or After March 15, 2015 [Member] Convertible Senior Subordinated Notes [Member] April 2009 Notes [Member]	Mar. 31, 2012 Holder [Member] Convertible Senior Subordinated Notes [Member] April 2009 Notes [Member]	Mar. 31, 2012 Holder [Member] On October 15, 2014, October 15, 2019 or Upon a Change in Control [Member] Convertible Senior Subordinated Notes [Member] October 2004 Notes [Member]	Mar. 31, 2012 Holder [Member] On March 15, 2015, March 15, 2020 or Upon Change in Control [Member] Convertible Senior Subordinated Notes [Member] February 2005 Notes [Member]	Oct. 17, 2011 October 2011 Debt Redemption [Member] Convertible Senior Subordinated Notes [Member] October 2004 Notes [Member]	May 31, 2011 May 2011 Debt Repurchase [Member] Convertible Senior Subordinated Notes [Member] October 2004 Notes [Member]	Sep. 30, 2011 May 2011 Debt Repurchase [Member] Convertible Senior Subordinated Notes [Member] October 2004 Notes [Member]	Jul. 20, 2010 July 2010 Refinancing Exchange [Member] Convertible Senior Subordinated Notes [Member] New Notes [Member]	Sep. 30, 2010 July 2010 Refinancing Exchange [Member] Convertible Senior Subordinated Notes [Member] New Notes [Member]	Sep. 30, 2010 July 2010 Refinancing Exchange [Member] Convertible Senior Subordinated Notes [Member] Old Notes [Member]	Jul. 20, 2010 July 2010 Refinancing Exchange [Member] Convertible Senior Subordinated Notes [Member] October 2004 Notes [Member]	Jul. 20, 2010 July 2010 Refinancing Exchange [Member] Convertible Senior Subordinated Notes [Member] February 2005 Notes [Member]	Mar. 31, 2012 Common Shares [Member] Convertible Senior Subordinated Notes [Member] October 2004 Notes [Member]	Mar. 31, 2012 Common Shares [Member] Convertible Senior Subordinated Notes [Member] February 2005 Notes [Member]	Mar. 31, 2012 Common Shares [Member] Convertible Senior Subordinated Notes [Member] April 2009 Notes [Member]	Jan. 11, 2012 Common Shares [Member] Convertible Senior Subordinated Notes [Member] January 2012 Notes [Member]	Mar. 31, 2012 Common Shares [Member] Minimum [Member] Convertible Senior Subordinated Notes [Member] October 2004 Notes [Member]	Mar. 31, 2012 Common Shares [Member] Minimum [Member] Convertible Senior Subordinated Notes [Member] February 2005 Notes [Member]	Mar. 31, 2012 Common Shares [Member] Minimum [Member] Convertible Senior Subordinated Notes [Member] April 2009 Notes [Member]	Mar. 31, 2012 Common Shares [Member] Maximum [Member] Convertible Senior Subordinated Notes [Member] October 2004 Notes [Member]	Mar. 31, 2012 Common Shares [Member] Maximum [Member] Convertible Senior Subordinated Notes [Member] February 2005 Notes [Member]	Mar. 31, 2012 Common Shares [Member] Maximum [Member] Convertible Senior Subordinated Notes [Member] April 2009 Notes [Member]	Jul. 20, 2010 Common Shares [Member] July 2010 Refinancing Exchange [Member] Convertible Senior Subordinated Notes [Member] New Notes [Member]
Principal amount of notes														$ 150,000,000				$ 175,000,000				$ 66,600,000		$ 45,000,000
Debt instrument, repurchase amount																																			27,000,000	19,500,000
Principal amount of notes repurchased	125,000																																		26,600,000	19,400,000
Gain (loss) on extinguishment of debt, before write-off of deferred debt financing cost																																							(14,500,000)
Write-off of deferred debt financing costs																																					100,000		600,000
Coupon rate									2.9375%	3.625%	2.9375%	2.9375%	2.9375%		3.625%	3.625%	3.625%		3.625%	3.625%	3.625%		4.00%			4.00%
Equity component											50,100,000				53,000,000				16,200,000				10,100,000
Loss on extinguishment of debt	(967,000)	(14,505,000)	5,675,000			(967,000)	(14,505,000)	5,675,000																													(500,000)
Principal amount of debt outstanding	1,159,585,000					135,393,000	136,377,000				348,000	46,326,000			23,464,000	23,470,000			66,581,000	66,581,000			45,000,000		0
Carrying value of debt outstanding	1,117,050,000	407,054,000				104,498,000	107,255,000				348,000	44,728,000			23,464,000	22,107,000			45,462,000	40,420,000			35,224,000		0
Carrying value of notes extinguished																																			26,600,000	18,900,000
Debt instrument redemption price percentage																													100.00%	100.00%	100.00%	100.00%	100.00%	100.00%	100.00%
Principal amount of notes exchanged																																									63,700,000	36,000,000
Conversion rate of number of common shares of the company per $1,000 principal amount of new notes																																											86.9565	70.0133	121.2121								161.2903
Debt instrument, denomination amount						1,000																																1,000
Conversion price per share											$ 11.50				$ 14.28				$ 8.25				$ 10.50																				$ 11.50	$ 14.28	$ 8.25	$ 10.50							$ 6.20
Extended put rights for New Notes, term																																						2 years
Amount of common shares the New Notes were converted into																																																					16,236,305
Increase to common shares equity from conversion of notes				67,620,000	38,403,000																																		106,000,000
Debt instrument, increase (decrease) of carrying amount																																								$ 91,200,000
Applicable price range for make-whole premium																																															$ 8.79	$ 10.35	$ 5.36	$ 50.00	$ 75.00	$ 50.00
Debt instrument, periodic payment, interest rate																			3.625%								3.625%	3.125%