Shareholders' Equity And Earnings Per Share (Market Value Of Company Common Stock And Settlement Rate) (Detail) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Applicable Market Value Of Company Common Stock Less Than Or Equal To 30 Dollars [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Settlement Rate, per share		1.6666
Market Value Of Common Stock Greater Than Thirty Dollars But Less Than Thirty Seven Point Five Zero Dollars [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Settlement Rate, Market Value	50.00	50.00
Applicable Market Value Of Company Common Stock Greater Than Or Equal To 37.50 Dollars [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Settlement Rate, per share		1.3333
Minimum [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Settlement Rate, per share		1.3333
Minimum [Member] | Applicable Market Value Of Company Common Stock Less Than Or Equal To 30 Dollars [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Applicable Market Value Of Company Common Stock Per Share	30.00
Minimum [Member] | Market Value Of Common Stock Greater Than Thirty Dollars But Less Than Thirty Seven Point Five Zero Dollars [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Applicable Market Value Of Company Common Stock Per Share	30.00
Minimum [Member] | Applicable Market Value Of Company Common Stock Greater Than Or Equal To 37.50 Dollars [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Settlement Rate, per share	1.3333
Maximum [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Settlement Rate, per share		1.6666
Maximum [Member] | Applicable Market Value Of Company Common Stock Less Than Or Equal To 30 Dollars [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Settlement Rate, per share	1.6666
Maximum [Member] | Market Value Of Common Stock Greater Than Thirty Dollars But Less Than Thirty Seven Point Five Zero Dollars [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Applicable Market Value Of Company Common Stock Per Share	37.5
Maximum [Member] | Applicable Market Value Of Company Common Stock Greater Than Or Equal To 37.50 Dollars [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Applicable Market Value Of Company Common Stock Per Share	37.5