Equity and Equity Units Offering - Additional Information (Detail) (USD $)	1 Months Ended		3 Months Ended
	Apr. 30, 2012	Mar. 30, 2009	Mar. 31, 2013 Y	Jun. 30, 2010	Mar. 15, 2012
Equity and Equity Units Offering Disclosure [Line Items]
Common shares sold from treasury stock		14,700,000
Equity units number issued, units		6,600,000
Common shares sold aggregate stated amount	$ 106,273,000	$ 235,000,000
Equity units sold aggregate public offering price		165,000,000
Forward purchase price contract obligation per share		$ 25
Undivided beneficial ownership interest		2.50%
Senior notes principal amount		1,000
Senior notes interest rate		8.00%			3.854%
Purchase contract settlement date			2012-04-30
Senior notes maturity			2014
Fair value of purchase contract per unit at issuance		$ 3.75
Senior notes fair value, per note		$ 21.25
Period at end of which notes will be stated on balance sheet at face amount, in years			3
Allocation of underwriting commissions as deferred charges		1.00%
Underwriting commissions paid, total		6.00%
Underwriting commissions allocated to equity forward		5.00%
Senior notes, final maturity date after which reset interest rate is applicable			Apr. 30, 2014
Common shares issued in exchange for equity units				2,300,000
Equity units outstanding				4,250,920
Senior notes coupon yield per annum					2.875%
Shares issued in exchange under purchase contracts	5,800,000