ISSUANCE OF 7 1/2% SERIES E PERPETUAL PREFERRED SHARES AND REDEMPTION OF SERIES A AND B PERPETUAL PREFERRED SHARES - Offerings (Detail) (USD $)	3 Months Ended				9 Months Ended						0 Months Ended	9 Months Ended	0 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013 Cumulative Redeemable Preferred Stock, Series E [Member]	May 16, 2013 Cumulative Redeemable Preferred Stock, Series E [Member]	Jun. 13, 2013 Series A And Series B Preferred Stock [Member]	Sep. 30, 2013 Series A And Series B Preferred Stock [Member]	Jun. 13, 2013 Series A Perpetual Preferred Shares [Member]	Jun. 13, 2013 Series B Perpetual Preferred Share [Member]
Class of Stock [Line Items]
Redeemable preferred stock, shares issued (in shares)										6,800,000
Redeemable preferred stock, face value										$ 170,000,000
Preferred Stock, Dividend Rate, Percentage (in hundredths)									7.50%
Redeemable preferred stock, liquidation preference per share (in dollars per share)										$ 25.00
Preferred Stock, Redemption Price Per Share (in dollars per share)										$ 25.00
Proceeds from Issuance of Redeemable Preferred Stock									164,300,000
Cash on hand paid to redeem preferred stock									42,700,000
Preferred Stock, Redemption Date												Jun. 13, 2013
Preferred Stock, Redemption Shares (in shares)													77,199	16,461,340
Preferred Stock, Shares Outstanding (in shares)													109,050	31,769
Common stock, shares, issued on conversion of preferred stock (in shares)													180,799	20,345
Cash used for redemption of preferred stock											207,000,000
Redemption preference premiums paid	$ 0	[1]	$ 0	[1]	$ 19,924,000	[1]	$ 0	[1]			$ 19,900,000
Premium paid per share reduction in earnings (in dollars per share)												$ 0.21

[1] The Series A and Series B preferred shares were redeemed on June 13, 2013 – See NOTE 9.