The value of an offering program (at the market, "ATM) that provides a potentially efficient means of raising measured amounts of equity capital over time by allowing a company to tap into the existing secondary market for its shares on an as-and-when-needed basis.

No definition available.

Preferred Stock - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended	3 Months Ended
	Sep. 14, 2012	Dec. 31, 2014	Dec. 31, 2012	Dec. 31, 2013	Sep. 30, 2012	Dec. 30, 2014	Dec. 30, 2013	Oct. 18, 2012	Mar. 31, 2015
Auction Market Preferred Securities, Stock Series [Line Items]
Preferred Stock Redeemed		375els_PreferredStockRedeemed
Preferred Stock, shares authorized		10,000,000
Preferred Stock, par value per share		$ 0.01		$ 0.01
Common Stock, Par or Stated Value Per Share		$ 0.01		$ 0.01
At The Market Offering Value					$ 125.0els_AtMarketOfferingValue
Preferred Stock, Shares Authorized		9,765,900us-gaap_PreferredStockSharesAuthorized		9,765,525us-gaap_PreferredStockSharesAuthorized
Preferred Stock, Shares Issued		0us-gaap_PreferredStockSharesIssued		0us-gaap_PreferredStockSharesIssued
Peferred Stock, Shares Exchanged	5,445,765els_PeferredStockSharesExchanged
Depositary Shares, Issued	5,445,765els_DepositarySharesIssued
Depositary Share, Liquidation Preference Per Share	$ 25.00
Preferred Stock, Dividend Rate, Per-Dollar-Amount	$ 0.3849625
Cumulative Series D Six Percent Non-Qualified Preferred Stock [Member]
Auction Market Preferred Securities, Stock Series [Line Items]
Preferred Stock, par value per share		$ 0.01		$ 0.01
Preferred Stock, Dividend Rate, Percentage		6.00%
Preferred Stock, Shares Authorized		179,639		179,764
Preferred Stock, Shares Issued		0		125		125	125
Preferred Stock, Liquidation Preference Per Share							$ 1,000.00
Cumulative Series E Eighteen Point Seven Five Percent Nonvoting Preferred Stock [Member]
Auction Market Preferred Securities, Stock Series [Line Items]
Preferred Stock, par value per share		$ 0.01		$ 0.01
Preferred Stock, Dividend Rate, Percentage		18.75%
Preferred Stock, Shares Authorized		0		250
Preferred Stock, Shares Issued		0		250		250	250
Preferred Stock, Liquidation Preference Per Share							$ 1,000.00
Cumulative Series C Six Point Seven Five Percent Redeemable Perpetual Preferred Stock [Member]
Auction Market Preferred Securities, Stock Series [Line Items]
Preferred Stock, par value per share		$ 0.01		$ 0.01
Preferred Stock, Dividend Rate, Percentage		6.75%
Preferred Stock, Shares Authorized	54,458	54,461		54,461
Preferred Stock, Shares Issued		54,458		54,458
Preferred Stock, Liquidation Preference Per Share	$ 2,500.00
Cumulative Series Eight Point Zero Three Four Percent Redeemable Perpetual Preferred Stock [Member]
Auction Market Preferred Securities, Stock Series [Line Items]
Preferred Stock, Liquidation Preference Per Share								$ 25.00
Preferred Stock, Dividend Rate, Per-Dollar-Amount			$ 0.0948460
Stock Redeemed or Called During Period, Shares			2,554,235
Stock Redeemed or Called During Period, Value			$ 64.1
Subsequent Event [Member] \| Cumulative Series D Six Percent Non-Qualified Preferred Stock [Member]
Auction Market Preferred Securities, Stock Series [Line Items]
Preferred Stock, Shares Authorized									179,639