Subsequent Event - Additional Information (Detail) (USD $)	3 Months Ended	1 Months Ended	3 Months Ended	1 Months Ended		1 Months Ended
	Mar. 31, 2013	Apr. 30, 2013 Subsequent Event [Member]	Mar. 31, 2013 Global Facility [Member]	Apr. 30, 2013 Global Facility [Member] Subsequent Event [Member]	Apr. 30, 2013 Senior Notes Due June Two Thousand Thirteen [Member] Subsequent Event [Member]	Apr. 30, 2013 Two Point Six Two Five Percent Exchangeable Notes [Member] Subsequent Event [Member]
Subsequent Event [Line Items]
Public offering common shares		35,650,000
Share price		$ 41.60
Number of shares exercised by underwriters	214,343	4,650,000
Repayment of outstanding borrowings				$ 470,900,000
Proceeds from debt				1,400,000,000
Repurchase of outstanding principal amount					$ 202,300,000	$ 341,000,000
Percentage of exchangeable notes						2.625%
Exchangeable notes due date			Jun. 03, 2015			May 15, 2038