Shareholders' Equity And Earnings Per Share (Narrative) (Detail) (USD $)	0 Months Ended	1 Months Ended	3 Months Ended		12 Months Ended			1 Months Ended							1 Months Ended			3 Months Ended	12 Months Ended			12 Months Ended		12 Months Ended
	Dec. 19, 2008	Mar. 31, 2012	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2010	Dec. 07, 2010	Dec. 31, 2012 HPK Financial Corporation [Member]	Aug. 31, 2012 Great Lakes Advisors, Inc [Member]	Jul. 31, 2011 Great Lakes Advisors, Inc [Member]	Aug. 31, 2008 Series A Preferred Stock [Member]	Mar. 31, 2013 Series A Preferred Stock [Member]	Dec. 31, 2012 Series A Preferred Stock [Member]	Mar. 31, 2012 Series A Preferred Stock [Member]	Mar. 31, 2012 Series C Preferred Stock [Member]	Mar. 31, 2013 Series C Preferred Stock [Member]	Dec. 31, 2012 Series C Preferred Stock [Member]	Mar. 31, 2013 Market Value Of Common Stock Greater Than Thirty Dollars But Less Than Thirty Seven Point Five Zero Dollars [Member]	Dec. 31, 2012 Market Value Of Common Stock Greater Than Thirty Dollars But Less Than Thirty Seven Point Five Zero Dollars [Member]	Dec. 31, 2012 Maximum [Member]	Mar. 31, 2013 Maximum [Member] Market Value Of Common Stock Greater Than Thirty Dollars But Less Than Thirty Seven Point Five Zero Dollars [Member]	Dec. 31, 2012 Minimum [Member]	Mar. 31, 2013 Minimum [Member] Market Value Of Common Stock Greater Than Thirty Dollars But Less Than Thirty Seven Point Five Zero Dollars [Member]	Dec. 31, 2010 Equity [Member]
Temporary Equity [Line Items]
Tangible equity unit, proceeds							4,600,000
Rate on tangible equity units							7.50%
Tangible equity unit public offering price per unit							$ 50.00
Net proceeds on sale of tangible equity units						$ 222,700,000
Debt Instrument, Maturity Date			Dec. 15, 2013			Dec. 15, 2013
Percentage of fair value of debt component quarterly cash payments						7.50%
Discount rate on debt component							9.50%
Risk-free rate			0.70%	0.70%																				0.95%
Expected stock price volatility minimum																								35.00%
Expected stock price volatility maximum																								45.00%
Percent of dividend yield plus stock borrow cost																								0.85%
Equity term, years			4 years 6 months	4 years 6 months																				3 years 7 days
Junior subordinated amortizing note, initial principal amount							9.728182
Quarterly installments on amortizing note						0.9375
Extended installment period on amortizing note			Dec. 15, 2015
Settlement rate, shares																				1.6666		1.3333
Applicable Market Value Of Company Common Stock Per Share																					$ 37.5		$ 30.00
Amount Reclassifed from Additional Paid in Capital to Common Stock Per Share					$ 1.00
Number Of Consecutive Trading Days			20 days		20
Preferred stock, liquidation value per share											$ 1,000	$ 1,000	$ 1,000	$ 1,000	$ 1,000	$ 1,000	$ 1,000
Liquidation of preference shares, equity offering											$ 50,000,000				$ 126,500,000
Preferred stock, dividend rate, percentage											8.00%				5.00%
Convertible preferred stock conversion rate of common stock to Series A preferred stock											38.88				24.3132
Preferred stock, shares issued											50,000	50,000	50,000	50,000	126,500	126,500	126,500
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	1,643,295		1,643,295
Investment Warrants, Exercise Price	$ 22.82
Warrant Termination Period	10 years
Common Stock, shares issued in acquisition								372,530	25,493	529,087
Warrants holders common stock purchase price per share			$ 30.50
Warrants exercised		18,000
Warrants outstanding		1,000	0	1,000
Warrants expiration date			Feb. 01, 2013
Settlement Rate, Market Value																		50.00	50.00